test(node): add watcher churn stress target

[ChengShiLiu16]

Summary

Adds a focused Node SDK watcher churn stress target for the macOS FSEvents / debouncer crash reported in #603.

This does not claim to fix the crash. It gives maintainers a closer repro/diagnostic loop for the failing path: Node SDK + watcher enabled + concurrent filesystem churn + concurrent searches.

Changes

• Add packages/fff-node/test/watcher-churn-stress.mjs
  • creates a temp watched tree
  • starts FileFinder with the watcher enabled
  • waits for scan and watcher readiness
  • mutates files with create/write/rename/delete churn
  • concurrently runs file, directory, and grep searches
  • writes per-iteration fff logs under /tmp
• Add make test-node-watcher-stress
• Add make build-c-lib-prof, make prepare-node-prof, and make test-node-watcher-stress-prof
  • uses the existing profile.prof profile so macOS crashes can be reproduced with debuginfo/symbols retained

Validation

Local:

• node --check packages/fff-node/test/watcher-churn-stress.mjs
• npm ci --ignore-scripts
• cd packages/fff-node && npm run build
• git diff --check
• make -n test-node-watcher-stress-prof

Not run locally:

• make test-node-watcher-stress
• make test-node-watcher-stress-prof

Reason: the local Rust toolchain currently has no usable cargo component and rustup rolls back while installing due to a rust-analyzer component conflict. The new Makefile targets expand correctly and should run in a working Rust environment / CI.

Refs #603

[dmtrKovalenko]

not sure what you mean but this is not reproducible for me not for mac not on linux