fix: allow lazy TLS init for threads started before profiling

[nsavoire]

What does this PR do?

When profiling starts on a process with already-running threads calling pthread_getattr_np, the allocation tracker's TLS state may not be initialized yet. This adds a pthread_getattr_np hook that guards against deadlock withthe following sequence:
(pthread_getattr_np -> malloc -> tracker -> init_tl_state -> save_context -> pthread_getattr_np deadlock) and enables lazy TLS init in get_tl_state() when safe.

Motivation

Allow allocation profiling of existing threads when profiler is not started at process startup.

[pr-commenter]

Benchmark results for collatz

Parameters

	Baseline	Candidate
config	baseline	candidate
profiler-version	ddprof 0.24.0+978f4be5.105195233	ddprof 0.24.0+780ea42a.105213418

Summary

Found 0 performance improvements and 0 performance regressions! Performance is the same for 1 metrics, 0 unstable metrics.

See unchanged results

scenario	Δ mean execution_time
scenario:ddprof -S bench-collatz --preset cpu_only collatz_runner.sh	same

[pr-commenter]

Benchmark results for BadBoggleSolver_run

Parameters

	Baseline	Candidate
config	baseline	candidate
profiler-version	ddprof 0.24.0+978f4be5.105195233	ddprof 0.24.0+780ea42a.105213418

Summary

Found 0 performance improvements and 0 performance regressions! Performance is the same for 1 metrics, 0 unstable metrics.

See unchanged results

scenario	Δ mean execution_time
scenario:ddprof -S bench-bad-boggle-solver BadBoggleSolver_run work 1000	same

[r1viollet]

I think the state.reentry_guard captures also when we are in an allocation hook ?

[r1viollet]

although this should not happen as we should never enter without a state, though this is a shared reentry mechanism

[nsavoire]

I reused state.reentry_guard since we don't use it when state is not yet initialized and the purpose is similar

[r1viollet]

Nicolas had a smart idea, the scenario we are worried about is doing an init while we already have a lock (allocation) held. This can happens when you are doing an mmap within a malloc (especially as we can not hook all mallocs).
His proposal was to only perform the init on APIs where it is impossible for us to hold a lock (like inside a malloc hook).
This is a great idea!