Video extraction is prone to race conditions

[cenodis]

tumblr-backup 1.0.5 via pip
tumblr-backup --save-video --save-audio keirastarlightdraconequus

After applying the fix in #35 tumblr-backup will properly execute yt-dlp to download videos.
However neither yt-dlp nor youtube-dl handle races when used in a multithreaded/multiprocessing environment [1]. This results in errors and (maybe?) file corruption.

This is especially frequent in blogs that reblog their own video posts close to each other, such as the customary 12-hour timezone reblog.

The best thing would be for tumblr-backup to handle these conflicts directly. It already resolves the target filename in get_youtube_url and could manage collisions using it as a key. This could also be used to filter out previously failed video URLs and help reduce unecessary yt-dlp calls.

[1] yt-dlp/yt-dlp#1918

Example errors:

ERROR: [youtube] f6ehAm9Ib-o: Video unavailableo 5199 (of 7288 expected)        
Unable to download video in post #146853269595                                  
ERROR: file:<REDACTED>/keirastarlightdraconequus/media/eFX04e9FuYM_@PitchandMagpieProductions_My_Secret_Weapon_MLP_Comic_Reading.f397.mp4: No such file or directory
ERROR: Unable to rename file: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f137.mp4.part' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f137.mp4'
ERROR: Unable to rename file: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f137.mp4.part' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f137.mp4'
ERROR: Unable to rename file: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f137.mp4.part' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f137.mp4'
ERROR: Unable to rename file: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f140.m4a.part' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f140.m4a'
ERROR: Unable to rename file: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f140.m4a.part' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f140.m4a'
ERROR: Unable to rename file: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f137.mp4.part' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f137.mp4'
ERROR: Unable to rename file: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f140.m4a.part' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.f140.m4a'
ERROR: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.temp.mp4' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.mp4'
WARNING: Cannot update utime of file
WARNING: Cannot update utime of file
ERROR: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.temp.mp4' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.mp4'
ERROR: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.temp.mp4' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.mp4'
WARNING: Cannot update utime of file
ERROR: [Errno 2] No such file or directory: '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.temp.mp4' -> '<REDACTED>/keirastarlightdraconequus/media/k6xD1S4NfLU_@thewildcardperson_Molestia_vs_Discord_animation.mp4'
ERROR: [youtube] 5-bQE3WMzGA: Private video. Sign in if you've been granted access to this video. Use --cookies-from-browser or --cookies for the authentication. See  https://github.com/yt-dlp/yt-dlp/wiki/FAQ#how-do-i-pass-cookies-to-yt-dlp  for how to manually pass cookies. Also see  https://github.com/yt-dlp/yt-dlp/wiki/Extractors#exporting-youtube-cookies  for tips on effectively exporting YouTube cookies
Unable to download video in post #144696447150