Enable pyupgrade in ruff and fix the issues that pop up

[dalonsoa]

Description

pyupgrade is now enabled in ruff, using python 3.9 as the target since we want to keep the compatibility with it. As usual with these things, a lot of files are changed, but otherwise you should only worried about pyproject.toml.

Fixes #293

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s.

• [x] New feature (non-breaking change which adds functionality)
• [ ] Optimization (non-breaking, back-end change that speeds up the code)
• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] Breaking change (whatever its nature)

Key checklist

• [x] All tests pass: $ python -m pytest
• [x] The documentation builds and looks OK: $ python -m sphinx -b html docs docs/build

Further checks

• [x] Code is commented, particularly in hard-to-understand areas
• [ ] Tests added that prove fix is effective or that feature works

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 74.26710% with 79 lines in your changes missing coverage. Please review.

Project coverage is 71.24%. Comparing base (9938ba9) to head (e2e6888).

Files	Patch %	Lines
src/muse/readers/csv.py	40.47%	18 Missing and 7 partials :warning:
src/muse/outputs/mca.py	42.10%	7 Missing and 4 partials :warning:
src/muse/regressions.py	47.05%	9 Missing :warning:
src/muse/investments.py	40.00%	1 Missing and 5 partials :warning:
src/muse/examples.py	80.00%	3 Missing :warning:
src/muse/production.py	57.14%	1 Missing and 2 partials :warning:
src/muse/agents/factories.py	71.42%	0 Missing and 2 partials :warning:
src/muse/hooks.py	75.00%	0 Missing and 2 partials :warning:
src/muse/interactions.py	71.42%	0 Missing and 2 partials :warning:
src/muse/objectives.py	75.00%	1 Missing and 1 partial :warning:
... and 11 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #356 +/- ## =========================================== + Coverage 71.14% 71.24% +0.09% =========================================== Files 44 44 Lines 5844 5870 +26 Branches 1158 1158 =========================================== + Hits 4158 4182 +24 - Misses 1364 1366 +2 Partials 322 322 ```

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