Remove temporary files

[JPTIZ]

There are some files that are created by pico-bot that are never deleted automatically (example:

pico-bot/picobot/handlers.py

Line 419 in 033e461

video_path = MEDIA_DIR / f'{VIDEO_PREFIX}{user_id}.webm'

). They should be some kind of cleanup.

We could either use a context-manager like autodelete(path) where these files are used (to ensure they'll be deleted upon cleanup) or use stdlib's tempfile (as they're temporary files used only to upload videos to Telegram).