Add split recording support

[partouf]

Summary

• Detects recording file splits via the ffmpeg muxer's file_changed signal
• Creates a new log file for each recording segment with reset timing
• Checks output plugin ID (ffmpeg_muxer / ffmpeg_mpegts_muxer) before connecting, gracefully skips unsupported outputs
• Works with both sync-with-video and strftime filename modes

Closes #68

Test plan

1. Enable file splitting in OBS:

   • Go to Settings → Output → Recording
   • Check "Automatically split recording files"
   • Set a split condition — easiest for testing is "Split by file size" with a small size like 10–50 MB, or "Split by time" with a short duration like 1–2 minutes

2. Configure InfoWriter:

   • Add an "Info Writer" source if you don't have one
   • Enable "Sync with video file name and path" for the best test — each split video file should get a matching log file
   • Alternatively, use a strftime filename like /tmp/obslog_%Y%m%d_%H%M%S.txt

3. Record for long enough to trigger at least one split. When the split happens, verify that:

   • The first log file has a Stop entry at the split point
   • A new log file appears matching the new video segment
   • The new log file starts with EVENT:RECORDING SPLIT - NEW FILE and timing resets to 0
   • Any hotkeys/scene changes after the split go to the new file

4. Also test without splitting to make sure normal recording still works as before:

   • Regular start/stop recording produces correct output
   • Hotkeys and scene changes still work normally

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