### all
- reduce redundant code
- add `_` to some inner calls
### core
- rename `check_model` to `has_loaded`
- new api `download_models`
- move vocos out of models dict (further target: remove the dict `pretrain_models`)
- new api `unload`
- new api `decode_to_wavs`
### model
- fix grad mul issue in dvae
- optimize progress bar display
- optimize tensor operations