Use probe-rs MemoryInterface::read() to make reads go faster

[jamesmunns]

As a follow-up to #721, we realized that probe-rs changes have made read_u8 actually do u8 reads, which makes our bulk reading operations roughly 4x slower.

This switches to the new MemoryInterface::read() API, which does word-size reads (with some potential over-/under-reading), which we believe matches the old read_8 behavior.

This has a noticable speed improvement for flash --verify:

jamesmunns@lurch ~ $ humility --version
humility 0.12.18 
jamesmunns@lurch ~ $ time pfexec humility -a ./build-grapefruit-a-image-default-master.zip -t grapefruit-sp flash --verify
humility: WARNING: archive on command-line overriding archive in environment file
humility: attaching with chip set to "STM32H753ZITx"
humility: attached to 0d28:0204:00000080488fa31e569f0cd2389b3d90c84efe104c504355 via CMSIS-DAP
humility: verified 563.50 KiB in 11 seconds
humility: verified auxflash in slot 2
humility flash failed: archive is already flashed on attached device; use -F ("--force") to force re-flash

real    0m12.621s
user    0m3.926s
sys     0m1.307s

# master pre-#721
jamesmunns@lurch ~ $ time pfexec ./humility-0807 -a ./build-grapefruit-a-image-default-master.zip -t grapefruit-sp flash --verify
humility: WARNING: archive on command-line overriding archive in environment file
humility: attaching with chip set to "STM32H753ZITx"
humility: attached to 0d28:0204:00000080488fa31e569f0cd2389b3d90c84efe104c504355 via CMSIS-DAP V2 IF: 4 DESC: Some(InterfaceAltSetting { interface_number: 4, alternate_setting: 0, num_endpoints: 2, class: 255, subclass: 0, protocol: 0, string_index: Some(9), endpoints: [Endpoint { address: 0x05, direction: Out, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }, Endpoint { address: 0x85, direction: In, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }] })
humility: verifying 577024 bytes at 0x8000000
humility: verified 563.50 KiB in 42 seconds
humility: verified auxflash in slot 2
humility flash failed: archive is already flashed on attached device; use -F ("--force") to force re-flash

real    0m44.414s
user    0m5.487s
sys     0m3.616s

# master post-#721
jamesmunns@lurch ~ $ time pfexec ./humility-0807-fast -a ./build-grapefruit-a-image-default-master.zip -t grapefruit-sp flash --verify
humility: WARNING: archive on command-line overriding archive in environment file
humility: attaching with chip set to "STM32H753ZITx"
humility: attached to 0d28:0204:00000080488fa31e569f0cd2389b3d90c84efe104c504355 via CMSIS-DAP V2 IF: 4 DESC: Some(InterfaceAltSetting { interface_number: 4, alternate_setting: 0, num_endpoints: 2, class: 255, subclass: 0, protocol: 0, string_index: Some(9), endpoints: [Endpoint { address: 0x05, direction: Out, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }, Endpoint { address: 0x85, direction: In, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }] })
humility: verifying 577024 bytes at 0x8000000
humility: verified 563.50 KiB in 22 seconds
humility: verified auxflash in slot 2
humility flash failed: archive is already flashed on attached device; use -F ("--force") to force re-flash

real    0m24.510s
user    0m5.394s
sys     0m3.575s

# this branch
jamesmunns@lurch ~ $ time pfexec ./humility-0807-faster -a ./build-grapefruit-a-image-default-master.zip -t grapefruit-sp flash --verify
humility: WARNING: archive on command-line overriding archive in environment file
humility: attaching with chip set to "STM32H753ZITx"
humility: attached to 0d28:0204:00000080488fa31e569f0cd2389b3d90c84efe104c504355 via CMSIS-DAP V2 IF: 4 DESC: Some(InterfaceAltSetting { interface_number: 4, alternate_setting: 0, num_endpoints: 2, class: 255, subclass: 0, protocol: 0, string_index: Some(9), endpoints: [Endpoint { address: 0x05, direction: Out, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }, Endpoint { address: 0x85, direction: In, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }] })
humility: verifying 577024 bytes at 0x8000000
humility: verified 563.50 KiB in 7 seconds
humility: verified auxflash in slot 2
humility flash failed: archive is already flashed on attached device; use -F ("--force") to force re-flash

real    0m8.589s
user    0m3.683s
sys     0m1.295s

As well as for dump:

# 0.12.18
jamesmunns@lurch ~ $ time pfexec humility -a ./build-grapefruit-a-image-default-master.zip -t grapefruit-sp dump
humility: WARNING: archive on command-line overriding archive in environment file
humility: attached to 0d28:0204:00000080488fa31e569f0cd2389b3d90c84efe104c504355 via CMSIS-DAP
humility: core halted
humility: dumping to "hubris.core.0"
humility: dumped 910.38 KiB in 17 seconds
humility: core resumed

real    0m19.461s
user    0m4.488s
sys     0m2.048s

# master pre-#721
jamesmunns@lurch ~ $ time pfexec ./humility-0807 -a ./build-grapefruit-a-image-default-master.zip -t grapefruit-sp dump
humility: WARNING: archive on command-line overriding archive in environment file
humility: attached to 0d28:0204:00000080488fa31e569f0cd2389b3d90c84efe104c504355 via CMSIS-DAP V2 IF: 4 DESC: Some(InterfaceAltSetting { interface_number: 4, alternate_setting: 0, num_endpoints: 2, class: 255, subclass: 0, protocol: 0, string_index: Some(9), endpoints: [Endpoint { address: 0x05, direction: Out, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }, Endpoint { address: 0x85, direction: In, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }] })
humility: core halted
humility: dumping to "hubris.core.1"
humility: dumped 910.38 KiB in 68 seconds
humility: core resumed

real    1m11.501s
user    0m7.066s
sys     0m5.829s

# master post-#721
jamesmunns@lurch ~ $ time pfexec ./humility-0807-fast -a ./build-grapefruit-a-image-default-master.zip -t grapefruit-sp dump
humility: WARNING: archive on command-line overriding archive in environment file
humility: attached to 0d28:0204:00000080488fa31e569f0cd2389b3d90c84efe104c504355 via CMSIS-DAP V2 IF: 4 DESC: Some(InterfaceAltSetting { interface_number: 4, alternate_setting: 0, num_endpoints: 2, class: 255, subclass: 0, protocol: 0, string_index: Some(9), endpoints: [Endpoint { address: 0x05, direction: Out, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }, Endpoint { address: 0x85, direction: In, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }] })
humility: core halted
humility: dumping to "hubris.core.2"
humility: dumped 910.38 KiB in 36 seconds
humility: core resumed

real    0m39.589s
user    0m7.174s
sys     0m5.780s

# this branch
jamesmunns@lurch ~ $ time pfexec ./humility-0807-faster -a ./build-grapefruit-a-image-default-master.zip -t grapefruit-sp dump
humility: WARNING: archive on command-line overriding archive in environment file
humility: attached to 0d28:0204:00000080488fa31e569f0cd2389b3d90c84efe104c504355 via CMSIS-DAP V2 IF: 4 DESC: Some(InterfaceAltSetting { interface_number: 4, alternate_setting: 0, num_endpoints: 2, class: 255, subclass: 0, protocol: 0, string_index: Some(9), endpoints: [Endpoint { address: 0x05, direction: Out, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }, Endpoint { address: 0x85, direction: In, transfer_type: Bulk, max_packet_size: 512, packets_per_microframe: 1, interval: 0 }] })
humility: core halted
humility: dumping to "hubris.core.3"
humility: dumped 910.38 KiB in 11 seconds
humility: core resumed

real    0m13.785s
user    0m4.221s
sys     0m2.043s

[labbott]

Some minor comments but LGTM. I think this is relatively low risk since arguably we are going back to the behavior we had before (and there's zero change to the net behavior)