feat: test for send & sync

[George-Miao]

No description provided.

[Berrysoft]

LGTM

[Copilot]

Pull request overview

This PR adds compile-time tests for Send and Sync trait bounds on multithreaded synchronization primitives by introducing an AssertMt trait, adds a CONTRIBUTING.md file with contribution guidelines, and removes unused Display trait implementations from atomic types.

Key changes:

• Introduces AssertMt trait to verify Send + Sync bounds on sync module types
• Adds explicit unsafe Send/Sync implementations for mutex and bilock internal types
• Adds project contribution guidelines in CONTRIBUTING.md

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/lib.rs	Defines the AssertMt trait as a compile-time assertion for Send + Sync bounds
src/mutex/mod.rs	Adds explicit Send/Sync implementations for mutex types and AssertMt test for Mutex
src/bilock/mod.rs	Adds Send/Sync implementations for Inner and AssertMt tests for BiLock, BiLockAcquire, and BiLockGuard
src/mutex_blocking.rs	Adds AssertMt test for blocking Mutex wrapper around std::sync::Mutex
src/waker_slot.rs	Adds AssertMt test for WakerSlot (futures::task::AtomicWaker)
src/flag.rs	Adds AssertMt test for atomic boolean Flag
src/event.rs	Adds AssertMt tests for Event and EventListener types
src/atomic/unsync.rs	Removes Display trait implementations for AtomicBool and atomic integer types
CONTRIBUTING.md	Adds comprehensive contribution guidelines covering development workflow and style guide

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