fix: reset popover saving state

[flying3615]

Problem:
Popover cell editors would get stuck in a "saving" state if reopened after a successful save. This was caused by
stale React state persisting in component instances that were reused by ag-grid for performance.

Solution:
A useEffect hook was added to GridPopoverContextProvider. It triggers whenever the editor is opened and reliably
resets the component's internal state (e.g., saving and hasSaved), ensuring the editor is always in a clean state.

Author Checklist

• appropriate description or links provided to provide context on the PR
• self reviewed, seems easy to understand and follow
• reasonable code test coverage
• change is documented in Storybook and/or markdown files

Reviewer Checklist

• Follows convention
• Does what the author says it will do
• Does not appear to cause side effects and breaking changes
  • if it does cause breaking changes, those are appropriately referenced

Post merge

• Post about the change in #lui-cop

Conventional Commit Cheat Sheet:
build: Changes that affect the build system or external dependencies (example scopes: gulp, broccoli, npm)
ci: Changes to our CI configuration files and scripts (example scopes: Circle, BrowserStack, SauceLabs)
docs: Documentation only changes
feat: A new feature
fix: A bug fix
perf: A code change that improves performance
refactor: A code change that neither fixes a bug nor adds a feature
test: Adding missing tests or correcting existing tests