feat: go watcher

[AlliBalliBaba]

This is an experimental branch, moving the watcher to a go-only library (https://github.com/sgtdi/fswatcher).

Not sure if worth it yet, but would potentially simplify dependencies (like not needing libstdc++).

[nickchomey]

FWIW, i'd welcome this change. I wonder if some watcher-related issues might be addressed at the same time?

#2095
#2572
#2708
#2568

[AlliBalliBaba]

I'll first have to verify the tradeoffs of using this watcher.

But yeah we can add an exclusion pattern. I think #2572 might have already been fixed on main, haven't tried it myself. Moving the watcher to go would also fix #2708 (and hopefully not introduce other issues...). #2568 is an issue in the pecl HTTP extension and needs a fix there (not thread safe on shutdown).

[AlliBalliBaba]

Nvm, I had big hopes for sgtdi/fswatcher, but I couldn't get it to not crash CI or leak memory on Linux. Let's wait for a better go watcher implementation.