Backport of "libav: Fix compatibility with ffmpeg 7" into 1.24

Backport of !6505 (merged) "libav: Fix compatibility with ffmpeg 7".

Todo:

• Needs manual intervention, cherry-picking failed!

Commits:

• 9d465d9e avdemux: Remove typefinder implementation
• 0871a55c libav: Fix signature of avprotocol write function for ffmpeg 7
• aab2f59d avviddec: Rename variables and fuse function (bonus backport of !6851 (merged) to avoid conflicts)
• 73d0cac1 libav: Update AVCodecContext lifetime to work properly with ffmpeg 7
• 2a3f791c avdemux: Fix leak of demuxer input context in error cases
• 03465d09 avmux: Reset input context to NULL after closing in the muxer
• ee518b9c avvidenc: Only use 2 ticks per frame if encoding interlaced video
• dc0aebbe avvidenc: Set the DTS to 0 if it is negative, not the PTS
• 1953bc61 avviddec: Only use 2 ticks per frame if decoding interlaced video
• e52f0bbc avvidenc: Make sure to pass always increasing PTS to the encoder
• a7bba83d typefind: Add typefinders for formats that were previously available via ffmpeg