Issue #83: Require Python 3.9

[Mark2000]

Description

Closes #83

Enforce python >=3.9 in setup.

How should this pull request be reviewed?

• By commit
• All changes at once

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

N/A; should probably be tested with CI server eventually

• Unit tests (General Environment only) pytest --cov bsk_rl/envs/general_satellite_tasking --cov-report term-missing tests/unittest
• Integrated tests (General Environment only) pytest --cov bsk_rl/envs/general_satellite_tasking --cov-report term-missing tests/integration

Test Configuration

• Python: 3.10.1
• Basilisk: N/A
• Platform: MacOS 3.11

Checklist:

• My code follows the style guidelines of this project (passes Black, ruff, and isort)
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Commit messages are atomic, are in the form Issue #XXX: Message and have a useful message
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes