Sticker-convert

- Add option for padding (`--padding-percent`)
- Allow auto retry for telegram down/upload
- Fix deadlock if no files to compress
- Fix hanging during cancel job on Windows

- Fix job random hanging
- Remove opt_comp_experiment
- Code cleanup

- Fix first frame getting dropped
- Fix importing gif/webp/apng with variable frame durations
- Calculate mean color frame by frame instead of combining to one large array, saving memory
- Fix webp collapsing same frames, causing incorrect timestamps
- Avoid overwritting frame in pyav
- Remove wheel as build dependency

- Fix not trying to compress lowest step
- Pad odd dimension video in pyav instead of resizing and causing blur
- Fix png being decoded by pyav
- Decode gif with pillow

- Add `--custom-presets` option
- Auto load custom_presets.json from config directory for providing custom compression presets

Convert frames to alpha=0 or 255 first before creating gif