node-api: fix crash on re-entering TSFN finalization during env shutdown

[legendecas]

Fix the TSFN finalization re-entrance. state = kClosed marks a TSFN as ready to be
deleted, so a TSFN should not set this state before calling into user code synchronously,
which could call into napi_release_threadsafe_function, and delete the TSFN
synchronously in the middle of ThreadSafeFunction::MaybeDelete.

Fixes: #65100

[nodejs-github-bot]

Review requested:

• @nodejs/gyp
• @nodejs/node-api

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.17%. Comparing base (b805fb5) to head (043d783).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_api.cc	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #65967   +/-   ##
=======================================
  Coverage   90.17%   90.17%           
=======================================
  Files         771      771           
  Lines      265489   265471   -18     
  Branches    50471    50470    -1     
=======================================
- Hits       239405   239397    -8     
  Misses      17042    17042           
+ Partials     9042     9032   -10     

Files with missing lines	Coverage Δ
src/node_api.cc	75.48% <66.66%> (+0.15%)	⬆️

... and 33 files with indirect coverage changes

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[KevinEady]

We discussed this PR in the 11 Sep 2026 Node-API meeting, specifically regarding of this MaybeDelete() can be called where the state is already kClosed (ie. if this MaybeDelete() gets called multiple times).

We discussed that it might be beneficial to add more test cases to verify that this CHECK_EQ is safe, by adding a test case with >1 for initial_thread_count and using the multiple pathways to "finalize" the TSFN:

• all threads call napi_release_threadsafe_function with napi_tsfn_release mode.
• one thread calls napi_release_threadsafe_function with napi_tsfn_abort, and other threads call napi_call_threadsafe_function which returns napi_closing.