Add homemade rwlock for no_std

[kigawas]

Inspired by #139

[Copilot]

Pull Request Overview

This PR introduces a custom spinlock-based reader-writer lock implementation for no_std environments, replacing the parking_lot dependency when the std feature is not enabled.

• Implements RawSpinRwLock using atomic operations and compare-exchange primitives
• Adds conditional compilation to use the custom rwlock in no_std mode while keeping parking_lot for std builds
• Updates Cargo.toml dependencies to make parking_lot optional and adds lock_api

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/sync.rs	New module implementing spinlock-based reader-writer lock with comprehensive tests
src/lib.rs	Conditionally includes sync module for no_std builds
src/config.rs	Imports custom RwLock for no_std, parking_lot for std builds
Cargo.toml	Makes parking_lot optional, adds lock_api dependency, updates std feature

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[Copilot]

Using Relaxed ordering for the initial load may miss recent state changes from other threads. Consider using Acquire ordering to ensure visibility of writes from unlock operations.

Suggested change

	let mut state = self.state.load(Ordering::Relaxed);
	let mut state = self.state.load(Ordering::Acquire);

[kigawas]

That's not correct, Ordering::Acquire is used compare_exchange_weak

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5cf33d8) to head (28875d8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##            master      #140    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           11        12     +1     
  Lines          489       661   +172     
==========================================
+ Hits           489       661   +172     

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