DRAFT: Streaming Datagrid

[martinRenou]

Provide a new widget StreamingDatagrid which lazily requests data to the back-end upon scrolling/resizing the grid. It only requests data needed to render the current viewport.

This is a very early draft for discussion, it requires more testing.

Screencast from 2024-04-08 11-34-30.webm

Wish-list for this PR to be merge-able:

• [ ] Filtering/sorting should be done back-end side by default for StreamingDatagrid, simply because the front-end does not have the whole dataset. We may want to provide the ability to do back-end filtering for the main Datagrid widget too, but front-end filtering should stay the default to not break current applications.
• [ ] Unit testing + Galata testing
• [x] Fix row headers
• [x] Provide a tick method to the Python API to allow the back-end to notify the front-end the data has changed
• [ ] Fix nested hierarchy support