fix(widgets): useWidget cleanup and add StrictMode test

[ibgreen]

For https://openjs-foundation.slack.com/archives/C05JCDKHQUE/p1763426667707549

Summary

• ensure useWidget removes widgets regardless of index so the first widget cleans up correctly
• add a React StrictMode regression test verifying widgets are not duplicated after remount

Testing

• yarn test node --filter react/deckgl.spec.ts

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Codex Task

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Note

Fixes useWidget cleanup to remove widgets at index 0 and adds a React StrictMode test to prevent duplicate widgets after remount.

• Bug Fix
  • In modules/react/src/utils/use-widget.ts, correct cleanup condition to remove the widget even when its index is 0, then update deck props.
• Tests
  • Extend test/modules/react/deckgl.spec.ts with a React StrictMode test component using useWidget to verify only one widget remains after StrictMode remount.

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