PR #306 split: publish AML global-lock mutex fix

[SnowCheetos]

Context

This tracks the second small replacement PR split out from rust-osdev#306, addressing rust-osdev#305.

The global-lock bugfix is useful independently and should not be bundled with allocator API work.

Scope

Publish the existing local branch:

• codex/pr306-global-lock
• commit da1e0ec (aml: balance global lock mutex handling)

Included changes:

• Return early from acquire_global_lock and release_global_lock when no FACS is present.
• Re-acquire the AML-side global-lock mutex before retrying after firmware contention.
• Release the AML-side global-lock mutex in release_global_lock.
• Add tests/global_lock.rs to assert handler acquire/release calls balance.

Out of scope

• Allocator API work.
• Platform allocator fixes.
• Version bumps.
• Formatting-only churn.

Acceptance criteria

• Branch is pushed to the fork.
• PR is opened against rust-osdev/acpi:main and references AML global lock acquisition of global_lock_mutex looks wrong rust-osdev/acpi#305.
• rustfmt --edition 2024 --check src/aml/mod.rs tests/global_lock.rs passes.
• cargo test --test global_lock passes.
• cargo test --lib passes.