fix: prefetch video_image when getting a video

[viadanna]

Description

This pull request updates the way related course and image data are fetched for videos in the edxval/api.py module, optimizing the database query for retrieving a Video by including video image data.

This prevents the number of database queries during video serialization from increasing with the number of CourseVideo objects pointing to the Video object.

Testing instructions

1. Ensure a devstack or sandbox with a course containing a video referenced in edx-val's CourseVideo.
2. Ensure at least two CourseVideo objects are pointing to the same Video. Export the course and import to a new one to get another CourseVideo reference.
3. Enable SQL logging by adding the following settings:

# Enable database logging
LOGGING["formatters"]["db"] = {"format": "[%(name)s] %(filename)s:%(lineno)d - %(message)s"}
LOGGING["loggers"]["django.db.backends"] = {
    "handlers": ["local"],
    "level": "DEBUG",
    "formatter": "db"
}

4. Open a django shell and try serializing a video

In [2]: from edxval import api

In [3]: api.CourseVideo.objects.last()
Out[3]: <CourseVideo: course-v1:edx+demo+a>

In [4]: api.CourseVideo.objects.last().__dict__
Out[4]: 
{'_state': <django.db.models.base.ModelState at 0x72276ed650d0>,
 'id': 24,
 'course_id': 'course-v1:edx+demo+a',
 'video_id': 31,
 'is_hidden': False}

In [5]: api.Video.objects.get(id=31)
Out[5]: <Video: 88723157-d381-46ff-8f3c-324970fcea3e>

In [6]: api.get_video_info("88723157-d381-46ff-8f3c-324970fcea3e")

Out[6]: {'encoded_videos': [OrderedDict([('created', datetime.datetime(2026, 2, 19, 19, 5, 59, 251724, tzinfo=datetime.timezone.utc)), ('modified', datetime.datetime(2026, 2, 19, 19, 5, 59, 251820, tzinfo=datetime.timezone.utc)), ('url', 'https://example.com/file.mp4'), ('file_size', 32619768), ('bitrate', 261), ('profile', 'mobile_low')]), OrderedDict([('created', datetime.datetime(2026, 2, 19, 19, 5, 59, 251934, tzinfo=datetime.timezone.utc)), ('modified', datetime.datetime(2026, 2, 19, 19, 5, 59, 252129, tzinfo=datetime.timezone.utc)), ('url', 'https://d2f1egay8yehza.cloudfront.net/ASUASM24/ASUASM24T315-V005300_MB1.mp4'), ('file_size', 61681723), ('bitrate', 493), ('profile', 'mobile_high')]), OrderedDict([('created', datetime.datetime(2026, 2, 19, 19, 5, 59, 252219, tzinfo=datetime.timezone.utc)), ('modified', datetime.datetime(2026, 2, 19, 19, 5, 59, 252256, tzinfo=datetime.timezone.utc)), ('url', 'https://example.com/file.mp4'), ('file_size', 123890767), ('bitrate', 991), ('profile', 'desktop_mp4')]), OrderedDict([('created', datetime.datetime(2026, 2, 19, 19, 5, 59, 252341, tzinfo=datetime.timezone.utc)), ('modified', datetime.datetime(2026, 2, 19, 19, 5, 59, 252374, tzinfo=datetime.timezone.utc)), ('url', 'hpZW8xlVbBE'), ('file_size', 0), ('bitrate', 0), ('profile', 'youtube')])], 'courses': [{'course-v1:edx+demo+paulo': None}, {'course-v1:edx+demo+a': None}], 'url': '/api/val/v0/videos/88723157-d381-46ff-8f3c-324970fcea3e', 'created': datetime.datetime(2026, 2, 19, 19, 5, 59, 232659, tzinfo=datetime.timezone.utc), 'edx_video_id': '88723157-d381-46ff-8f3c-324970fcea3e', 'client_video_id': 'file.mp4', 'duration': 999.53, 'status': 'imported', 'error_description': None}

5. Verify that multiple queries are made for the video image:

2026-02-26 14:57:54,376 DEBUG 72 [django.db.backends] utils.py:131 - (0.001) SELECT `edxval_video`.`id`, `edxval_video`.`created`, `edxval_video`.`edx_video_id`, `edxval_video`.`client_video_id`, `edxval_video`.`duration`, `edxval_video`.`status`, `edxval_video`.`error_description` FROM `edxval_video` WHERE `edxval_video`.`edx_video_id` = '88723157-d381-46ff-8f3c-324970fcea3e' LIMIT 21; args=('88723157-d381-46ff-8f3c-324970fcea3e',); alias=default
2026-02-26 14:57:54,378 DEBUG 72 [django.db.backends] utils.py:131 - (0.001) SELECT `edxval_encodedvideo`.`id`, `edxval_encodedvideo`.`created`, `edxval_encodedvideo`.`modified`, `edxval_encodedvideo`.`url`, `edxval_encodedvideo`.`file_size`, `edxval_encodedvideo`.`bitrate`, `edxval_encodedvideo`.`profile_id`, `edxval_encodedvideo`.`video_id`, `edxval_profile`.`id`, `edxval_profile`.`profile_name` FROM `edxval_encodedvideo` INNER JOIN `edxval_profile` ON (`edxval_encodedvideo`.`profile_id` = `edxval_profile`.`id`) WHERE `edxval_encodedvideo`.`video_id` IN (31); args=(31,); alias=default
2026-02-26 14:57:54,380 DEBUG 72 [django.db.backends] utils.py:131 - (0.001) SELECT `edxval_coursevideo`.`id`, `edxval_coursevideo`.`course_id`, `edxval_coursevideo`.`video_id`, `edxval_coursevideo`.`is_hidden` FROM `edxval_coursevideo` WHERE `edxval_coursevideo`.`video_id` IN (31); args=(31,); alias=default
2026-02-26 14:57:54,385 DEBUG 72 [django.db.backends] utils.py:131 - (0.001) SELECT `edxval_videoimage`.`id`, `edxval_videoimage`.`created`, `edxval_videoimage`.`modified`, `edxval_videoimage`.`course_video_id`, `edxval_videoimage`.`image`, `edxval_videoimage`.`generated_images` FROM `edxval_videoimage` WHERE `edxval_videoimage`.`course_video_id` = 12 LIMIT 21; args=(12,); alias=default
2026-02-26 14:57:54,388 DEBUG 72 [django.db.backends] utils.py:131 - (0.001) SELECT `edxval_videoimage`.`id`, `edxval_videoimage`.`created`, `edxval_videoimage`.`modified`, `edxval_videoimage`.`course_video_id`, `edxval_videoimage`.`image`, `edxval_videoimage`.`generated_images` FROM `edxval_videoimage` WHERE `edxval_videoimage`.`course_video_id` = 24 LIMIT 21; args=(24,); alias=default

6. Now deploy the changes from this PR, repeat the last two steps and verify the videoimage queries changed to a single outer join.

2026-02-26 15:04:09,333 DEBUG 184 [django.db.backends] utils.py:131 - (0.002) SELECT `edxval_coursevideo`.`id`, `edxval_coursevideo`.`course_id`, `edxval_coursevideo`.`video_id`, `edxval_coursevideo`.`is_hidden`, `edxval_videoimage`.`id`, `edxval_videoimage`.`created`, `edxval_videoimage`.`modified`, `edxval_videoimage`.`course_video_id`, `edxval_videoimage`.`image`, `edxval_videoimage`.`generated_images` FROM `edxval_coursevideo` LEFT OUTER JOIN `edxval_videoimage` ON (`edxval_coursevideo`.`id` = `edxval_videoimage`.`course_video_id`) WHERE `edxval_coursevideo`.`video_id` IN (31); args=(31,); alias=default

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