This PR adds initial support for displaying tables to the `markdown`
crate.

This allows us to render tables in Assistant 2:

| Before | After |
|
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|
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|
| <img width="1309" alt="Screenshot 2025-03-03 at 1 39 39 PM"
src="https://github.com/user-attachments/assets/ad7ada01-f35d-4fcf-a20c-deb42b55b34e"
/> | <img width="1297" alt="Screenshot 2025-03-03 at 3 38 21 PM"
src="https://github.com/user-attachments/assets/9b771126-30a0-479b-8c29-f5f572936f56"
/> |

There are a few known issues that should be addressed as follow-ups:

- The horizontal scrolling within a table is linked with the scrolling
of the parent container (e.g., the Assistant 2 thread)
- Cells are currently cut off entirely when they are too wide, would be
nice to truncate them with an ellipsis

Release Notes:

- N/A