Fix crash and enable GIF animation in markdown preview (zed-industries#53459)

Closes zed-industries#53426

Fixes a crash when previewing markdown with GIFs, and enables GIF
animation in the preview panel.

Two issues: a partially-decoded GIF could crash the preview, and GIFs in
markdown previews never animated.

The fix for GIFs with empty comment extensions (`21 fe 00`) was
implemented upstream in the `image-gif` crate (image-rs/image-gif#228)
and released as `gif 0.14.2`. This PR bumps the dependency so those GIFs
now render correctly in the markdown preview without any further changes
to Zed itself.

## Screenshot
Left=VS Code
Right=Zed


https://github.com/user-attachments/assets/7950abbc-1a79-4f01-a425-9595aa688325

Release Notes:

- Fixed a crash in certain scenarios when opening Markdown Preview with
GIFs.
- Added GIF animation support for Markdown Preview.

---------

Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>

Author: 2 people