fix(LRUCache): copy using deepcopy, and ensure the get_all function always terminates

[cmanallen]

@aliu39 discovered that under certain circumstances a process can get stuck in an infinite loop. Andrew fixed this by using deepcopy which prevents the infinite loop and fixes a bug where the LRU returns incorrect results. Additionally, I've added a terminating loop in case there are any future bugs we've missed.

Closes: #3862

Out of precaution, we disabled flagpole evaluation tracking Sentry while we wait for this to be merged.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.93%. Comparing base (fd56608) to head (2d67b97).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3861      +/-   ##
==========================================
+ Coverage   79.91%   79.93%   +0.02%     
==========================================
  Files         137      137              
  Lines       15401    15403       +2     
  Branches     2619     2620       +1     
==========================================
+ Hits        12307    12312       +5     
+ Misses       2221     2219       -2     
+ Partials      873      872       -1     

Files with missing lines	Coverage Δ
sentry_sdk/_lru_cache.py	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

[aliu39]

We found out the process will hang if you copy a LRUCache, then call get_all() on the original. It works as expected if you call get_all() on clones. Will add some coverage in FF tests for this case (fork a scope then read the flags on the original scope)

[antonpirker]

This has been released with version 2.19.2: https://github.com/getsentry/sentry-python/blob/master/CHANGELOG.md#2192