fix: ignore: parallel walker occasionally hangs if visitor panics (#3009)

[krapcys1-maker]

Fixes #3009

Summary

Fixes a nondeterministic hang in ignore parallel walk when visitor code panics.

Problem

WalkParallel::visit() / WalkParallel::run() could hang after a panic in visitor logic. The panic did not always terminate worker progression cleanly, leaving threads stuck in work retrieval loops.

Reproduction

From crates/ignore, run parallel tests repeatedly (as described in #3009) until a panic path is hit; on affected code this can hang.

What changed

• crates/ignore/src/walk.rs
• In Worker::run, wrap run_one(work) with std::panic::catch_unwind.
• On panic, call quit_now() before resume_unwind(payload) so all workers observe quit state and stop.

Why this works

The change preserves panic propagation while ensuring global worker shutdown is signaled on panic, preventing the hang/livelock behavior.

Validation

• cargo check --workspace
• cargo test -p ignore --lib -- --nocapture

Scope

Single-file, targeted fix in ignore worker loop.