chore: release v2.2.0

[github-actions]

🤖 New release

• rusty_alloc: 2.1.0 -> 2.2.0
• rusty_alloc-api: 2.1.0 -> 2.2.0

Changelog

rusty_alloc

2.2.0 - 2026-09-10

Fixed

• The small profile extended every page ONE BLOCK AT A TIME, so 100 % of
  allocations took the slow path. page_extend bounds its batch at 4 KiB of
  payload and computed that bound with a hardcoded shift whose constant term is
  really SEGMENT_SLICE_SIZE / 4096. At the shipped 64 KiB slice the literal
  was right; under --cfg ra_small_profile the slice is 4 KiB, so the bound
  was 256 bytes instead of 4 KiB — sixteen times too small. For a 512-byte
  class the batch computed to 0 and was clamped to 1, leaving every page with
  capacity == 1 and no second block for the fast path to find. Counted over
  100,000 alloc+free pairs at the small profile, entries into malloc_generic
  per op: 512 B 1.0000 -> 0.1250, 513 B 1.0000 -> 0.1667, 1 KiB 1.0000 ->
  0.2500, with page carve-and-retire churn falling from 195 per 100,000 to
  24/32/49. On a 32-bit host the 512-vs-513 step inverts from +8.6 % (slower)
  to −36 % (faster), about 1.9× faster at 512. Measured on silicon too
  — a XIAO ESP32-S3, main against the fix on one board with identical
  checksums and floor: 13.0 % faster on 32 B ping-pong, 15.7 % on a
  64-block mixed batch, 15.3 % on 8-512 B churn, and 1.1 % at 2,048 B,
  which is on the bin route this does not touch. Found by the Kairos RTOS
  report (docs/plans/finished/fixed-prim-small-step.md §8.7).
  The default geometry is unchanged — the derived constant equals the old
  literal there, and the all-features x86-64 assembly diff moves no executable
  function.

Added

• --cfg ra_generic_collect="64" | "4096" | "65536", so a bare-metal
  firmware can move the periodic-collect heartbeat. It is the only lever over a
  real trade — a sweep returns an empty page, and the next allocation of that
  class carves and extends a fresh one, so a short period costs page churn
  while a long one costs capacity — and it was unreachable: options::set is a
  no-op under ONE_REGION, and the option's own doc told firmwares to "change
  the default it is built with" when no cfg existed. The default does not move.
• prim::fixed::shape_of(size) -> Shape — page bytes, dedicated segments
  and direct_route, const and derived from the active geometry. Answers
  "which page kind, and how many region bytes, does this size cost", which
  region_stats() cannot because it reports over region extents.
  Shape::direct_route names a boundary that moves with POINTER WIDTH:
  SMALL_SIZE_MAX is 128 * size_of::<usize>(), so it is 1,024 on a 64-bit
  host and 512 on a 32-bit chip. The Kairos RTOS measured a 16 % step there on
  a device and could not reproduce it on a workstation for exactly that reason
  (docs/plans/finished/fixed-prim-small-step.md).

rusty_alloc-api

2.2.0 - 2026-09-10

Other

• release v2.2.0

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This PR was generated with release-plz.