fix: keep the edx_video_id for libraries

[AhtishamShahid]

Recreation of #282, which was blocked by a failing CLA check on the original author's commits. This PR re-applies the same change with commits authored under my (CLA-signed) account so the check can pass. All credit for the fix and tests belongs to @marslanabdulrauf.

Related Ticket

https://github.com/mitodl/hq/issues/12414 (MIT Internal)

Steps to reproduce the Issue:

1. Get video id from course videos
2. Create or go to any Library, add video component. Go to the video component, put the video id in and save (optionally publish)
3. Click edit again and the "Video ID" is missing now.
4. Strangely though you can see it in the "Advanced Details"
5. And in the preview we get "No playable video source"

Possible root cause:

For new runtime edxval edx_video_id is being set to None which causes no sources to be loaded, which leads to this "No playable video sources found." error.

Description

This pull request updates the handling of the edx_video_id field in the parse_xml_new_runtime method to improve video compatibility in content libraries. Instead of setting edx_video_id to None, the code now retains its value, ensuring that videos already present in the Video Asset Library (VAL) continue to work as expected.

• Video compatibility fix:
  • video.py: Updated parse_xml_new_runtime to retain the edx_video_id field, preventing issues where videos become unplayable or lose their ID in the editor after saving.

Merge checklist:
Check off if complete or not applicable:

• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Fixup commits are squashed away
• Unit tests added/updated
• Manual testing instructions provided
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets

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