[caglarpir]

Stacked on #933; review the last commit.

video_process DIR OUT, with a symbolic link in DIR to a video outside it, crashed with ValueError: '<target>' is not in the subpath of '<DIR>': the folder of the samples was named after the path of the video relative to DIR, both with their links resolved, and the video resolved to outside DIR. video_process_and_upload and sample_video crashed the same way. Given the link itself, the video was sampled into a folder named after the file it links to, while the samples were named after the link (OUT/video.mp4/link_0_000001.jpg), so that geotagging them by their videos (process OUT --geotag_source blackvue_videos --geotag_source_path DIR) found none of them and failed them all with MapillaryGeoTaggingError, as their names do not start with the name of the folder.

Make the paths absolute without resolving their links, with os.path.abspath(), where the folder of the samples is named (_normalize_path, _sample_dir) and where samples are matched to their videos (find_image_samples): the samples of DIR/link.mp4 are OUT/link.mp4/link_0_000001.jpg, whether DIR or the link is given. Two links to one video are still sampled once, as deduplicate_paths() still tells the videos found apart by their resolved paths. os.path.abspath() makes a path that does not exist absolute on Windows too, which Path.resolve() did not with Python 3.9 and 3.10, so _absolute(), the helper for that, goes.

With a link in DIR to a BlackVue video:

• video_process DIR OUT --video_sample_distance 50: 6 frames in OUT/link.mp4/, 6 ready (main: the traceback above, exit 1). The same with DIR relative, or given with .. in it; sample_video and video_process_and_upload --dry_run too.
• By interval every 2 s: 30 frames, with the same positions and times as the same video copied into DIR as a file; then process OUT --geotag_source blackvue_videos --geotag_source_path DIR: 30 ready.
• video_process DIR/link.mp4 OUT: OUT/link.mp4/link_0_000001.jpg, and geotagging them by the videos in DIR: 6 ready (main: 6 MapillaryGeoTaggingError).
• DIR itself a link to a folder: as on main, 30 frames in a folder named after the video, all geotagged.

Compared with main on process, video_process and process_and_upload --dry_run, on images and videos of many cameras with the default and other sources, the outputs and exit codes are the same.

Unit and integration tests, doctests, mypy --python-version 3.9, ruff check, ruff format --check and usort diff are clean.