146 bug voice activity detection import fails

[900miles]

Description

Fixes import errors by not initializing models until a function is called. Also, makes the errors more informative when they do happen.

Related Issue(s)

146

How Has This Been Tested?

Passes all unit tests, and also some spot checks for the imports described in #146

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have added tests to cover my changes. (N/A, original tests already cover these cases)
• [x] All new and existing tests passed.
• [x] My code follows the code style of this project.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 18.36735% with 40 lines in your changes missing coverage. Please review.

Project coverage is 63.79%. Comparing base (113721a) to head (2b12014). Report is 57 commits behind head on main.

Files with missing lines	Patch %	Lines
src/senselab/audio/tasks/text_to_speech/marstts.py	0.00%	4 Missing :warning:
...c/senselab/audio/tasks/text_to_speech/styletts2.py	0.00%	4 Missing :warning:
...rc/senselab/audio/tasks/speaker_diarization/api.py	25.00%	3 Missing :warning:
src/senselab/audio/tasks/speaker_embeddings/api.py	25.00%	3 Missing :warning:
src/senselab/audio/tasks/speech_enhancement/api.py	25.00%	3 Missing :warning:
src/senselab/audio/tasks/voice_cloning/api.py	25.00%	3 Missing :warning:
...nselab/audio/tasks/speaker_diarization/pyannote.py	0.00%	2 Missing :warning:
...elab/audio/tasks/speaker_embeddings/speechbrain.py	0.00%	2 Missing :warning:
...tasks/speaker_verification/speaker_verification.py	0.00%	2 Missing :warning:
...senselab/audio/tasks/speech_to_text/huggingface.py	0.00%	2 Missing :warning:
... and 7 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #208 +/- ## ========================================== + Coverage 60.24% 63.79% +3.55% ========================================== Files 113 119 +6 Lines 4017 4226 +209 ========================================== + Hits 2420 2696 +276 + Misses 1597 1530 -67 ```

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[900miles]

@fabiocat93 I've made some changes to address your comments. Let me know if it's good to merge now.