fix(prof): add missing "in-preloading" check to RSHUTDOWN

[realFlowControl]

Description

The profiler may crash when:

1. The profiler is enabled,
2. Allocation profiling is enabled (on by default),
3. The preloading feature of PHP is on,
4. And a custom memory handler other than Datadog's is used. This could be another profiler, debugger, or by setting the environment variable USE_ZEND_ALLOC to 0.

The profiler is not supposed to collect samples during preloading for technical reasons. However, RSHUTDOWN was missing the "in-preloading" check which would lead to a situation where some profile types could collect data even though in preloading. In allocation profiling, this would lead to a situation where if a customer has a custom memory handler (or uses USE_ZEND_ALLOC=0) the allocation profiler would crash in allocation::alloc_prof_rshutdown() when trying to reset the heap:

dd-trace-php/profiling/src/allocation.rs

Lines 273 to 274 in 46258ca

	// Safety: `unwrap()` is safe here, as `heap` is initialized in `RINIT`
	let heap = unsafe { (*zend_mm_state).heap.unwrap() };

Only the allocation profile types are known to be affected; the other types avoided this issue through other guards.

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.80%. Comparing base (46ec759) to head (5fced85).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #3037   +/-   ##
=========================================
  Coverage     74.80%   74.80%           
  Complexity     2781     2781           
=========================================
  Files           112      112           
  Lines         11017    11017           
=========================================
  Hits           8241     8241           
  Misses         2776     2776           

Flag	Coverage Δ
tracer-php	74.80% <ø> (ø)

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[pr-commenter]

Benchmarks [ profiler ]

Benchmark execution time: 2025-01-14 16:11:40

Comparing candidate commit 5fced85 in PR branch florian/fix-preloading-profiling with baseline commit 46ec759 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 28 metrics, 8 unstable metrics.

[morrisonlevi]

We went over the code together and the change looks good to us. The side-effects are a bit hard to reason about, maybe we can think of a way to represent invariants we need in code to help communicate these better in the future.