Watch worktrees with parcel and skip ignored directories

[thesiti92]

Fixes #1073.

On Linux, Node's recursive fs.watch adds an inotify watch for every file and every directory. The git directory watch also covered every managed review checkout under .git/dev-fast, plus objects and logs. The root watch covered gitignored directories such as node_modules. #982 only filtered events and never cut how many watches were registered, so one review could use up fs.inotify.max_user_watches for every process of the user.

Change

• Worktrees are watched with @parcel/watcher 2.6.0, which adds one inotify watch per directory, never per file. It loads on first use, and if it fails to load, the worktree re-inspects on every request, as a failed watcher did before.
• The root watch skips .git and the gitignored directories git reports (ls-files --others --ignored --exclude-standard --directory), so nested .gitignore, info/exclude and core.excludesFile all apply.
• The git directory watch skips objects, logs, lfs and dev-fast. Events there no longer count either.
• A directory that appears inside a tracked one, or a .gitignore or info/exclude change, re-reads the ignored list and re-subscribes.

Measured

Fedora 44 (QEMU), the 0.2.4 preview with this runtime swapped in. The fixture repo has a gitignored node_modules and three managed checkouts.

	before	after
Desktop review host	32,003	332
whiteboard server (headless)	31,999	328
After a new gitignored target/ with 2,000 directories	—	332 / 328

Edits to tracked files still update the review in both modes.

Notes

• Parcel's install script only builds from source when asked, so it stays disabled in allowBuilds. The prebuilt binaries arrive as optional dependencies. About 1.4 MB per platform.
• On macOS parcel reports changes after about 70 ms (FSEvents) instead of about 11 ms, so the tests that slept before refreshWorktrees now share a 200 ms wait.
• A new Linux-only test counts the process's inotify watches.