refactor(events): use vim.defaulttable in EventManager

[broken-pen]

Summary

Minor clean-up of EventManager by using vim.defaulttable instead of custom logic.

Related Issues

Extracted from #878

Changes

• fix a minor type issue in EventManager.init
• replace custom logic in EventManager.listen with vim.defaulttable

Checklist

I confirm that I have:

• Followed the Conventional Commits specification (e.g., feat: add new feature, fix: correct bug, docs: update documentation).
• My PR title also follows the conventional commits specification.
• Updated relevant documentation, if necessary.
• Thoroughly tested my changes.
• Added tests (if applicable) and verified existing tests pass with make test.
• Checked for breaking changes and documented them, if any.