feat: allow custom props on tables to persist

[RichardMisiak]

Summary

This PR updates tables so that custom props work on the table block.

Potentially fixes #1749

Disclaimer The updates to the library code (block.ts, nodeToBlock.ts) were made by Claude Sonnet 4.5 via Claude Code. I wrote the example app myself for testing.

Rationale

I need to store custom props on table blocks.

Having looked at the block code for tables further it looks like most of the functionality I'd need (e.g. custom rendering of a cell based on props) would require modifying the implementation of TiptapTableCell/TiptapTableNode. This is a much larger change than I am comfortable doing but I think being able to store props on the table can still be useful.

Changes

createTableBlockSpec now accepts an optional prop definition, which is then persisted

Impact

N/A

Testing

Manual testing was done via the example added in this PR. I was unsure about the correct place to add automated tests.

Screenshots/Video

Checklist

• Code follows the project's coding standards.
• Unit tests covering the new feature have been added.
• All existing tests pass.
• The documentation has been updated to reflect the new feature

Additional Notes

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