Close [BS-3066](https://linear.app/affine-design/issue/BS-3066/优化长note的展示和折叠)
- Enhanced the visibility behavior of hidden content in edgeless notes by:
- Showing hidden content when a note is being edited, even when it's outside the viewport
- Improving hover behavior with a delay when leaving from the bottom of the note
- Adding proper cleanup of hover timeouts when the component is disconnected
- Optimizing the viewport element to keep editing blocks or elements visible
## Testing
- Added new E2E test cases covering:
- Hover behavior on selected notes
- Content visibility during editing
- Viewport scrolling behavior
- Edge cases for content visibility
## Impact
This change improves the user experience when working with collapsed notes in edgeless mode by making the content more accessible and preventing accidental content hiding during editing.
<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit
- **Bug Fixes**
- Improved visibility of hidden content in edgeless notes when hovering near the bottom edge or editing the note, especially after resizing or clipping.
- **New Features**
- Enhanced hover behavior with delayed clearing based on mouse position to improve user experience.
- **Tests**
- Added new tests verifying hidden content visibility in edgeless notes during hover and editing, simulating diverse user interactions.
- **Chores**
- Added utilities to get and set viewport center for improved test control.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
