feat(profiling) allocation profiling for PHP ZTS

[realFlowControl]

Description

PROF-8922 / #2070

This PR will bring allocation profiling to ZTS versions of PHP. In the "there is another custom handler installed" code path we are using an UnsafeCell for a thread local which is the cheapest way (evaluated at compile time and not runtime), as this is in the hot path (every allocation and free would borrow check at runtime).
We could argue that the case of another extension that has custom handlers installed is nearly non existing, so we could also be better safe then sorry, but OTOH I could not get it to crash.

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-03-20 11:33:38

Comparing candidate commit 81fa090 in PR branch florian/allocation-zts with baseline commit 7c36868 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 18 metrics, 3 unstable metrics.

[codecov-commenter]

Codecov Report

Merging #2506 (f7b21b0) into master (fc050ce) will increase coverage by 1.16%.
Report is 5 commits behind head on master.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2506      +/-   ##
============================================
+ Coverage     75.91%   77.07%   +1.16%     
  Complexity     2563     2563              
============================================
  Files           241      215      -26     
  Lines         27020    23048    -3972     
  Branches        976        0     -976     
============================================
- Hits          20511    17765    -2746     
+ Misses         5989     5283     -706     
+ Partials        520        0     -520     

Flag	Coverage Δ
appsec-extension	?
tracer-extension	78.70% <ø> (ø)
tracer-php	75.06% <ø> (ø)

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see 26 files with indirect coverage changes

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[morrisonlevi]

I believe OnceCell with cell.get_or_init(|| unreachable!()) and re-creating the OnceCell on each request has good enough codegen to be able to use, and then we avoid the unsafe. Discussed this with Florian on Zoom and Slack.