[FFmpegExtractAudioPP] Fix --no-overwrites not working for post-processed files

- Make --no-overwrites option also prevent overwriting of post-processed files
- Fix buggy logic that checked for non-existent orig_path
- Add overwrites parameter to FFmpegExtractAudioPP constructor
- Add comprehensive tests for both --no-overwrites and --no-post-overwrites
- Maintain backward compatibility with existing --no-post-overwrites behavior

Fixes issue where --no-overwrites had no effect on extracted audio files

yt_dlp/__init__.py

@@ -653,6 +653,7 @@ def get_postprocessors(opts):
             'preferredcodec': opts.audioformat,
             'preferredquality': opts.audioquality,
             'nopostoverwrites': opts.nopostoverwrites,
+            'overwrites': opts.overwrites,
         }
     if opts.remuxvideo:
         yield {