Bump einops

Running `pytest` gives us this warning:

```
=============================== warnings summary ===============================
EveryVoice_841/lib/python3.12/site-packages/einops/einops.py:731
/gpfs/fs5/nrc/nrc-fs1/ict/others/u/tes001/TxT2SPEECH/EveryVoice_841/EveryVoice_841/lib/python3.12/site-packages/einops/einops.py:731: SyntaxWarning: invalid escape sequence '\s'
\sum_{c, d, g} x[a, b, c] * y[c, b, d] * z[a, g, k]

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
================== 334 passed, 1 warning in 165.62s (0:02:45) ==================
```

This should be fixable by bumping einops to a more recent version, ideally the latest.

Before doing the bump, we need to make sure it does not break training styletts2 models.

Find the dependency declaration for einops and identify the version currently used. Run pytest to confirm the warning is resolved, then verify that training styletts2 models still works without regressions. Done means the dependency is updated and the existing test suite and styletts2 training remain successful.

Written by the indexing model from the issue text.