Fix GH-13437: FPM: ERROR: scoreboard: failed to lock (already locked)

[bukka]

This changes locking for scoreboard to reduce contention between readers and adds retries for acquiring scoreboard for read.

[bukka]

This is an attempt to fix GH-13437 which seems to work in my testing. However it might be a bit too much for the actual bug fix - specifically reduction of reader contention might not be necessary here because I didn't see that much reader contention in my testing. There is mostly writer contention so it should be enough to just add retries but the question is impact on performance. I'm still not decided whether to target 8.2 at the end. It will need more testing though. And also need to do some clean up as I initially started just with atomics so there are some left overs in the code.

[bukka]

Btw there are few more issues with locking procs and optimizing atomics that I plan to look later too.