:sparkles: Remove Poetry, add Mixup, rework metrics, & improve code quality

[o-laurent]

• [x] Merge the metrics and code quality PRs
• [x] Improve the documentation
• [x] Improve the handling of the path in experiments @alafage
• [x] Fix #72

Postponed to another PR

• [-] Implement calibration for ensemble classification
• [-] Implement mixup for ensemble classification

[codecov[bot]]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (0ca6966) 98.39% compared to head (5966b7c) 98.63%.

Files	Patch %	Lines
torch_uncertainty/routines/regression.py	80.00%	4 Missing :warning:
torch_uncertainty/routines/classification.py	95.45%	0 Missing and 3 partials :warning:
torch_uncertainty/datamodules/abstract.py	97.67%	0 Missing and 2 partials :warning:
torch_uncertainty/models/mlp.py	81.81%	1 Missing and 1 partial :warning:
torch_uncertainty/__init__.py	97.56%	0 Missing and 1 partial :warning:
torch_uncertainty/baselines/deep_ensembles.py	83.33%	1 Missing :warning:
torch_uncertainty/optimization_procedures.py	96.55%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #70 +/- ## ========================================== + Coverage 98.39% 98.63% +0.23% ========================================== Files 71 77 +6 Lines 3607 3871 +264 Branches 426 472 +46 ========================================== + Hits 3549 3818 +269 - Misses 22 23 +1 + Partials 36 30 -6 ``` | [Flag](https://app.codecov.io/gh/ENSTA-U2IS/torch-uncertainty/pull/70/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ENSTA-U2IS) | Coverage Δ | | |---|---|---| | [cpu](https://app.codecov.io/gh/ENSTA-U2IS/torch-uncertainty/pull/70/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ENSTA-U2IS) | `98.63% <98.58%> (+0.23%)` | :arrow_up: | | [pytest](https://app.codecov.io/gh/ENSTA-U2IS/torch-uncertainty/pull/70/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ENSTA-U2IS) | `98.63% <98.58%> (+0.23%)` | :arrow_up: | 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=ENSTA-U2IS#carryforward-flags-in-the-pull-request-comment) to find out more.

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