Drop support for python 3.7

[lebrice]

• Drops support for Python 3.7:
• Updates the pre-commit hooks to include the --select=UP flag (pyupgrade equivalent with ruff)
• Updates the build workflow
• Removes unnecessary checks / imports from python 3.7

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 60.59%. Comparing base (6363e05) to head (981ffd4). Report is 23 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #95 +/- ## ========================================== + Coverage 52.49% 60.59% +8.10% ========================================== Files 9 9 Lines 1364 1368 +4 ========================================== + Hits 716 829 +113 + Misses 648 539 -109 ``` | [Flag](https://app.codecov.io/gh/mila-iqia/milatools/pull/95/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | Coverage Δ | | |---|---|---| | [integrationtests](https://app.codecov.io/gh/mila-iqia/milatools/pull/95/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | `?` | | | [unittests](https://app.codecov.io/gh/mila-iqia/milatools/pull/95/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | `60.59% <100.00%> (+9.93%)` | :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=mila-iqia#carryforward-flags-in-the-pull-request-comment) to find out more.

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