Fix isolate cleanup segfault

[Qard]

What does this PR do?:

Ensures heap profiler is stopped when thread cleanup occurs.

Motivation:

In Node.js 24.x, if you start a heap profiler and fail to stop it before the thread exits it will segfault. If a thread would stop for whatever reason without calling StopSamplingHeapProfiler first it will crash the entire process due to trying to remove an allocation observer while it's still active. The argument could be made that this might actually be a V8 bug, but you'll probably want a workaround in any case.

Here's the crash trace:

  Thread 0 Crashed:: MainThread
  0   libsystem_platform.dylib      0x18982a454 _platform_memmove + 244
  1   node                          0x1026a7734
  v8::internal::AllocationCounter::RemoveAllocationObserver(v8::internal::AllocationObserver*) + 144
  2   node                          0x102709b64
  v8::internal::HeapAllocator::RemoveAllocationObserver(v8::internal::AllocationObserver*,
  v8::internal::AllocationObserver*) + 64
  3   node                          0x102b14d50 v8::internal::SamplingHeapProfiler::~SamplingHeapProfiler()
   + 36
  4   node                          0x102af2f8c v8::internal::HeapProfiler::~HeapProfiler() + 88
  5   node                          0x102af3040 v8::internal::HeapProfiler::~HeapProfiler() + 12
  6   node                          0x1027224c8 v8::internal::Heap::TearDown() + 1252
  7   node                          0x102674744 v8::internal::Isolate::Deinit() + 964
  8   node                          0x1026742bc v8::internal::Isolate::Deinitialize(v8::internal::Isolate*)
   + 144
  9   node                          0x1023503a4 node::MultiIsolatePlatform::DisposeIsolate(v8::Isolate*) +
  28
  10  node                          0x102314a74 node::NodeMainInstance::~NodeMainInstance() + 60
  11  node                          0x10227ad2c node::Start(int, char**) + 612
  12  dyld                          0x189461d54 start + 7184

How to test the change?:

Stop a worker thread without stopping the heap profiler within it first.

[szegedi]

We did something similar in #215 for the time profiler already.

[Qard]

Ah, I didn't even look at the CPU profiler. I just saw the crash while working on react-pprof and saw a quick fix. 😅

[szegedi]

LGTM, one nit for a simplification

[nsavoire]

This might be similar to:
#212