src: let Environments on one isolate share a cleanup hook

[codebytere]

The process-global registry that #63985 put behind AddEnvironmentCleanupHook() / RemoveEnvironmentCleanupHook() is keyed on {isolate, fun, arg} with a CHECK that insertion succeeds, and the Environment is left out of the key on purpose. Two Environments that share an isolate and register the same hook abort on the second registration. The Node-API docs only forbid registering the same pair twice in one environment, and an addon calling napi_add_env_cleanup_hook(env, hook, NULL) from every environment it is loaded into is normal; Electron loads addons into several Environments on Blink's isolate (subframes, same-process child windows).

The registry is now a multimap keyed on arg whose entries carry the Environment. Adding the same hook twice to one Environment still aborts as documented. Removal prefers the current Environment's registration and otherwise takes the matching one from another Environment, so removing during GC without a current context keeps working, and it only looks at the current context when the isolate passed in is the calling thread's current one. Since the entry to drop after a hook has run can no longer be found by {isolate, fun, arg} alone, CleanupHookThunkRun() marks its entry as running and erases exactly that entry afterwards; removing a running entry (a hook removing itself, as ~ObjectWrap() does) is a no-op and the hook may register itself again, which keeps the use-after-free from #65630 fixed without caching the fields.

Tests: EnvironmentTest.SameCleanupHookInTwoEnvironmentsOnOneIsolate (aborted before), RemoveCleanupHookOfOtherEnvironmentOnSameIsolate (pins the cross-Environment fallback), CleanupHookRemovesItselfWhileRunning (kept as a guard for the #65630 case). test/addons, test/node-api and test/js-native-api pass.

Refs: #63985
Refs: #65630

---

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

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/76954/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/76959/

[codecov]

Codecov Report

❌ Patch coverage is 83.87097% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.13%. Comparing base (ccd648e) to head (df3574c).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/api/hooks.cc	83.87%	0 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65777      +/-   ##
==========================================
- Coverage   90.14%   90.13%   -0.01%     
==========================================
  Files         769      769              
  Lines      261626   261640      +14     
  Branches    49663    49674      +11     
==========================================
- Hits       235832   235826       -6     
- Misses      16805    16817      +12     
- Partials     8989     8997       +8     

Files with missing lines	Coverage Δ
src/api/hooks.cc	87.42% <83.87%> (-0.78%)	⬇️

... and 25 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/76983/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/76985/