src: run same-priority platform tasks in posting order

[codebytere]

TaskQueue<T> has been a std::priority_queue since #58047 so that worker tasks honor v8::TaskPriority. Its
comparator returns false for entry types without a priority member and for equal priorities, and the comment expects
that to keep insertion order. A binary heap doesn't: three tasks pushed A, B, C pop as A, C, B, and 64 pushes come back
out as 0, 2, 6, 14, 30, 62, ...

Three queues are affected: the per-isolate foreground queue (tasks of one priority no longer run in the order they were
posted), the foreground delayed queue, and the worker runner's DelayedTaskScheduler, where it can hang shutdown. That
scheduler drains its local queue in one batch, so when V8 posts a delayed worker task shortly before the platform shuts
down, the StopTask pushed by Stop() can run before a ScheduleTask that was pushed earlier; the ScheduleTask then
starts a timer on the scheduler's loop after all timers were stopped, and Shutdown() sits in uv_thread_join() until
the delay expires (8 s when the late task is the memory reducer). It shows up as an intermittent multi-second exit stall
in processes that exit soon after doing some work.

This is the other half of the shutdown race #61999 addressed: that change makes PostDelayedTask() return early once
Stop() has run (both under the tasks_ lock), so every ScheduleTask that is queued was queued before the StopTask;
with posting order restored it also runs before it, and no further flag is needed.

The fix gives every queued item a sequence number and uses it as the tie breaker, so equal-priority and priority-less
tasks come out FIFO again while higher priorities still go first; PopAll() returns the tasks in that order instead of
handing out the heap, which also removes the const_cast loops at its three call sites.

Tests: new cctest (TaskQueueTest.HigherPriorityFirstThenPostingOrder: FIFO across PopAll()/Pop() for a
priority-less queue, priority-then-FIFO for TaskQueueEntry) fails on main and passes here; cctest and the default
suite pass.

Refs: #58047
Refs: #61999

---

Disclosure: the code, test and this description were written by Claude Code, directed and reviewed by @codebytere.

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.12%. Comparing base (30bff4a) to head (121482b).
⚠️ Report is 27 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_platform.cc	94.73%	0 Missing and 1 partial ⚠️
src/node_platform.h	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65353      +/-   ##
==========================================
- Coverage   90.13%   90.12%   -0.02%     
==========================================
  Files         752      752              
  Lines      251568   251816     +248     
  Branches    47270    47348      +78     
==========================================
+ Hits       226759   226943     +184     
- Misses      16168    16176       +8     
- Partials     8641     8697      +56     

Files with missing lines	Coverage Δ
src/node_platform.cc	74.75% <94.73%> (-1.25%)	⬇️
src/node_platform.h	85.71% <80.00%> (-5.96%)	⬇️

... and 57 files with indirect coverage changes

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[jasnell]

Nit: The readability of this is... poor ;-) ... Might be better to split these lines up a bit.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/75958/