CI with `pytest_num_workers=8` for torch/tf jobs
We set `pytest_num_workers` to `3` for `torch_job` and 6 for `tf_job` to avoid OOM. With the recent efforts of reducing model size in CI, we can actually set `pytest_num_workers=8`.

- The full suite: all 3 jobs (PT/TF/Flax): `12-15 minutes`
- On the latest nightly CI (without all PRs merged today): `PT: 37 min | TF: 25 min | Flax: 20 min)`

The `torch_job` reach `95%` of RAM (peak), and `tf_job` is at `80%` of RAM. The `torch_job` with `n8` is a bit dangerous, but I think I have a way to further improve things in follow PR(s).
_The documentation is not available anymore as the PR was closed or merged._