fix: fuels from their inputs; bolt v1.12.0

[noah-emp]

bolt 1.12.0 widens the fuel rule (U006) to a U32.to_nat(<literal>) fuel. That flags 15 sites here (#128). Each is fixed as follows.

Now derived from the input

• pkg/pkg.bend of: the walk over a whole checkout takes walk.fuel(fs). That is one step for the entry plus one per line of every file, because every import is a line. This is the same measure the add and publish walks already use. A checkout of any size is walked whole, with no 100000-step cut.
• pkg/pkg.bend pkg.ask's inner walk: resumed.fuel(tree, st) is the length of the queue still pending plus walk.fuel of the files read so far.
• io/file.bend read.opened: the opened file's size comes from File.size, and the read takes size / 64 KiB + 2 reads. A size of 0 (a pipe, a device or /proc) or a failed size (a file past 4 GiB) gives no size to go by, so those reads keep the old bound as unsized().

Kept as named, commented defs (no size known up front)

• The rounds() of the planner loops in add, doctor, fetch, lock, pub and tool keep their old values (100, 100000, 10, 100000, 100000, 100). Each round's questions come from the last round's answers. Running out dies loudly instead of cutting work short.
• pkg.ask's outer asks() (100000) covers the disk walk, which asks for one file a round and can't know the file count before reading.
• check/framing.bend and check/oracle.bend thousand() (1000 × 1000) keep the test servers' "forever".
• check/serve.bend reads() (4096 × 64 KiB): a request's length isn't known until its head arrives.

[tools.bolt] moves to v1.12.0. No SPEC row names any of these limits.

Gate:

• bolt 1.12.0 reports 0 errors. Its warnings are now 375, up from 365, all L001 on the new defs.
• ez prove passes 16/16.
• nix flake check -L passes.
• ez lock on ez itself leaves the lock byte-identical.
• ez --help and ez doctor work.
• src/pkg/main.bend gives a byte-identical hash and manifest for ez's main.bend, before and after.
• io/file.bend reads a 404000-byte file, /proc/self/status and an empty file back whole.

Closes #128

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