Adding custom model size for Whisper.cpp and Faster Whisper

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 63.49206% with 46 lines in your changes missing coverage. Please review.

Project coverage is 82.67%. Comparing base (4d06273) to head (865c316).

Files	Patch %	Lines
buzz/model_loader.py	55.55%	20 Missing :warning:
...ts/preferences_dialog/models_preferences_widget.py	69.76%	13 Missing :warning:
buzz/settings/settings.py	58.82%	7 Missing :warning:
...ets/transcriber/transcription_options_group_box.py	66.66%	5 Missing :warning:
buzz/transcriber/whisper_file_transcriber.py	75.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #820 +/- ## ========================================== - Coverage 83.07% 82.67% -0.41% ========================================== Files 85 85 Lines 4426 4530 +104 ========================================== + Hits 3677 3745 +68 - Misses 749 785 +36 ``` | [Flag](https://app.codecov.io/gh/chidiwilliams/buzz/pull/820/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams) | Coverage Δ | | |---|---|---| | [Linux](https://app.codecov.io/gh/chidiwilliams/buzz/pull/820/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams) | `81.94% <63.49%> (-0.39%)` | :arrow_down: | | [macOS](https://app.codecov.io/gh/chidiwilliams/buzz/pull/820/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams) | `82.00% <61.11%> (-0.46%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams#carryforward-flags-in-the-pull-request-comment) to find out more.

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