2025.10.17-canary.904

fix(editor): missing signal of optional flat props (#13762)

Close https://github.com/toeverything/AFFiNE/issues/13750

#### PR Dependency Tree


* **PR #13762** 👈

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Optional block properties are now supported (e.g., flat-table), with
default values applied automatically when not set.

* **Bug Fixes**
* More reliable initialization and syncing of block properties, ensuring
defaults appear consistently.
* Change notifications now correctly reflect updates to
optional/defaulted properties.

* **Tests**
* Added tests verifying optional property behavior, default application,
syncing, and change events.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->





#### PR Dependency Tree


* **PR #13762** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)