chore: release v2.0.1

[github-actions]

🤖 New release

• rusty_alloc: 2.0.0 -> 2.0.1 (✓ API compatible changes)
• rusty_alloc-api: 2.0.0 -> 2.0.1

Changelog

rusty_alloc

2.0.1 - 2026-09-08

Fixed

• (prim) refuse a region that cannot hold a segment, and diagnose reentrancy

Other

• (deps) pull portable-atomic only where it is reachable

Added

• prim::fixed::MIN_REGION and prim::fixed::usable_bytes(base, len) — a
  firmware can now size its heap region at COMPILE time
  (const _: () = assert!(N >= MIN_REGION)) instead of discovering the answer
  on silicon, and can log how much of a region can actually back segments. The
  k * SEGMENT_SIZE + FIXED_PAGE rule previously existed only in a design
  document; a 220 KiB region strands 24,576 bytes and nothing said so.
• Distinct prim::fixed error codes: FERR_TOO_SMALL, FERR_GEOMETRY,
  FERR_REGISTERED. One sentinel covered three conditions with three different
  fixes.

Fixed

• init_region accepted a region that could never yield a segment. Setting
  --cfg ra_single_threaded (which the crate demands loudly) without
  --cfg ra_small_profile (which nothing demanded) left SEGMENT_SIZE at
  32 MiB, so a kilobyte-scale region returned Ok(()), linked clean, and then
  failed every allocation on the board with a backtrace pointing at whatever
  allocated first. It now returns FERR_GEOMETRY, checked against the real base
  address rather than the length alone — an unaligned base needs up to
  SEGMENT_SIZE - 1 more than a length test would demand.

• An allocating interrupt handler hung the firmware silently.
  prim::fixed's lock is not reentrant, and on a single-context target a lock
  observed held can only mean reentrancy. That is now a panic naming the ISR
  instead of an unbounded spin that surfaces as a watchdog reset. Confirmed with
  a load, because compare_exchange_weak may fail spuriously and a bare CAS
  failure would misfire.

• The README documents --cfg ra_small_profile, which it never mentioned, and
  attaches it to the 68 KiB figure that is only true under it.

  All four reported by the first outside firmware to adopt 2.0.0
  (docs/plans/embedded-adoption.md).

rusty_alloc-api

2.0.0 - 2026-09-07

Breaking

• default-features = false now selects no_std. This crate's own source
  has been no_std since M2; only the core dependency's default features stood
  in the way. default = ["std"] is new, and turning it off gives a firmware
  the single-heap profile — which also requires --cfg ra_single_threaded on
  the core. Consumers on default features are unaffected.

Added

• std feature (default-on) forwarding to rusty_alloc/std, so
  RustyAlloc can be a bare-metal #[global_allocator].

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This PR was generated with release-plz.