perf: use Lock for small boost and declare intent

[TimothyMakkison]

Small change, Lock is slightly faster that using object, but the main advantage is that it declares intent.

[thomhurst]

Summary

This PR replaces object lock instances with the modern Lock type for improved performance and clearer intent across 5 files in the TUnit.Core and TUnit.Engine projects.

Critical Issues

None found

Analysis

The changes are straightforward and appropriate.

What was changed:

• TUnit.Core/Tracking/ObjectTracker.cs:24
• TUnit.Engine/Scheduling/ConstraintKeyScheduler.cs:42, 133
• TUnit.Engine/Services/AfterHookPairTracker.cs:20-21
• TUnit.Engine/Services/BeforeHookTaskCache.cs:17-18
• TUnit.Engine/Services/TestDependencyResolver.cs:20

TUnit Rules Compliance:

• Performance First: The Lock type provides better performance than object for locking, aligning with TUnit's performance-first principle. These changes are in hot paths.
• AOT Compatible: Lock is fully AOT-compatible.
• Multi-targeting Support: The Polyfill package (v9.7.3) provides System.Threading.Lock polyfill for older target frameworks.
• No dual-mode concerns: Changes are only in TUnit.Engine and TUnit.Core, not in source generators.
• No snapshot updates needed: No source generator output or public API changes.

Verdict

APPROVE - Clean performance improvement with no issues. The change aligns perfectly with TUnit's Performance First and use modern features principles.