fix: cancel pending style manager updates on destroy

[sridharkalaibala]

Style Manager cancels its debounced selection refresh during destruction, but leaves two other callbacks queued: property updates and custom events. A style change followed immediately by editor destruction still invokes the property updater; a target change followed by module destruction still emits a custom event.

Retain both debounced functions and cancel them alongside upAll after stopping listeners. This keeps deferred work from running after teardown without changing live update behavior.

Related to #6494. I investigated the rapid create/destroy report but could not reproduce its original exception on the current build; this PR addresses the confirmed incomplete cleanup and intentionally does not close that issue.

Validation:

• Two regression cases fail on the original source and pass with the fix: pending property updates after editor destruction (with an actual styled selection) and custom events after module destruction. A live-update control passes in both versions.
• Full core suite: 1,530 tests and 17 snapshots pass; 47 existing tests skipped. The strengthened selection setup was also rerun in the focused suite.
• Core production build (JS, ESM, CSS and declarations), declaration type check, changed-file ESLint/Prettier, and diff checks pass.
• Chromium running the built editor completes ten create/select/style/destroy cycles without page errors. Instrumented methods forward to the originals and confirm no property/custom callbacks execute after destruction.

Prepared with AI assistance and validated locally using Node 24.19.0 and pnpm 9.10.0. No dependency, lockfile, or public API changes.