refactor: zod for props

[YousefED]

Summary

This PR drops our custom schema for Block and Inline Content Props and uses Zod instead.

Rationale

• Less "non-standard" code to maintain
• Easier to explain in docs / to LLMs

Changes

Impact

Consumers using custom blocks would need to migrate

• [ ] TODO: Determine if we want to accept old style props for backwards compatibility

Testing

Mostly by existing unit tests. TODO:

• [x] build of examples doesn't pass. couldn't figure out the build errors for withMultiColumn and withPageBreak examples. Playing around with BlockNoteSchema vs CustomBlockNoteSchema. Perhaps @nperez0111 can help here?
• [ ] Manual testing + code review. @matthewlipski can you help with this (after build + tests pass), and specifically the file blocks and anywhere where block type guards are used
• [ ] add tests / example for more complex schemas (e.g.: a prop with a nested object). @matthewlipski can you help?
• [ ] check compatibility with yjs, does it break with https://github.com/yjs/y-prosemirror/issues/116? (cc @nperez0111)
• [ ] heading props / customization (marked as TODO)

Screenshots/Video

N/A

Checklist

• [x] Code follows the project's coding standards.
• [ ] Unit tests covering the new feature have been added.
• [x] All existing tests pass.
• [ ] Y: The documentation has been updated to reflect the new feature
• [ ] Y: Review and add comments + followup work
• [ ] All: validate this doesn't make typescript / IDE significantly slower when developing
• [ ] All: Decide on zod as a dep or as a peer dep. Can we use standard schema?
• [ ] Check remaining comments in https://github.com/TypeCellOS/BlockNote/pull/2111

Additional Notes

Future work:

• [ ] Migrate style props as well?
• [x] Refactor File Blocks / File Props?
• [x] Remove / refactor "Partial" blocks as much as possible