[Audio] Remove torchaudio from spectrogram transforms
Overall LGTM, but needs documenting of all reshapes (e.g. via `einops`)
# What does this PR do ?

This PR removes use of `torchaudio` from `AudioToSpectrogram` and `SpectrogramToAudio`.
Classes using `torchaudio` are kept under `AudioToSpectrogamTA` and `SpectrogramToAudioTA`, similarly to `FilterbankFeatures` and `FilterbankFeaturesTA`.

**Collection**: audio

# Changelog 
- Removed `torchaudio` requirement for `AudioToSpectrogram` and `SpectrogramToAudio`
- Added unit tests to check analysis, synthesis, and reconstruction
- Added unit tests to check the update is matching `torchaudio` version

# Usage
* You can potentially add a usage example below

```python
# Prepare analysis and synthesis transforms
encoder = AudioToSpectrogram(fft_length=fft_length, hop_length=hop_length)
decoder = SpectrogramToAudio(fft_length=fft_length, hop_length=hop_length)

# Analysis transform, input shape (B, C, T)
X, _ = encoder(input=x)

# Synthesis transform, output shape (B, C, T)
y, _ = decoder(input=Y)
```

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