fix(inline-toolbar): preserve popover during selection refresh

[Sawtone]

Related to #2822.

This fix keeps the open inline-toolbar container mounted during selection refreshes, preventing flicker and repeated entrance animations. Tools and buttons are still recreated, preserving existing cleanup, including link handling. It also handles positioning, pending interactions, stale renders, and cleanup after render failures.

Validation

13/13 new and 54/54 existing related Cypress cases passed, plus 13/13 checks each in Chromium, Firefox, and WebKit. ESLint reports no errors; TypeScript has the same 719 baseline diagnostics. Tests loaded source through Vite; no distribution build or full local CI run was performed.

Flipper

The unchanged keyboard-navigation test failed in earlier runs on both unmodified v2.31.7 and the earlier prototype. Its 100ms wait can race the 180ms selection debounce, leaving currentBlock undefined; two retries did not consistently resolve it. Flipper remains untouched and was excluded from the final selected run.

More

Retaining tool/button instances could be a separate follow-up.

[Sawtone]

Updated the regression test for Firefox 115, where formatting an entire text node may not emit selectionchange. The test now explicitly triggers that event after applying/removing bold.