Use parking_lot in faulthandler - #6438

Walkthrough

Replaced std::sync::Mutex and Condvar with parking_lot equivalents throughout crates/stdlib/src/faulthandler.rs. Changed unwrap-based lock acquisitions to direct lock calls, updated condition variable wait patterns from wait_timeout to wait_for, and adjusted guard handling in the WATCHDOG state and unix-specific user_signals submodule. No public API changes.

Changes

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Verify parking_lot API semantics: Ensure lock(), wait_for(), and guard handling match previous std::sync behavior and do not introduce unexpected differences in timeout or blocking semantics
• WATCHDOG state mutations: Confirm all WATCHDOG state access patterns are correctly updated and thread-safe
• Condition variable semantics: Validate that wait_for() timeout behavior is equivalent to the previous wait_timeout() pattern
• Guard scope and lifetime: Review all guard variable scope changes to ensure no new deadlock or guard drop timing issues

Possibly related PRs

• Faulthandler #6400 — Introduces Watchdog/WATCHDOG synchronization mechanisms in faulthandler.rs; this PR updates those same lock primitives to use parking_lot
• Faulthandler #6406 — Modifies faulthandler.rs state and handler code; this PR refactors synchronization for the same module

Suggested reviewers

• ShaharNaveh

Poem

🐰 The parking lot beckons, no waits in sight,
Mutexes swapped for speed, threading feels light,
No unwrapping panics on these guarded doors,
Fault handlers synced—now running much more! ✨

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