Update to Python 3.12

[douglatornell]

• [x] Add Python 3.12 to GHA pytest-with-coverage workflow so that we can use the workflow to test whether all the packages NEMO-Cmd depends on have been updated to support Python 3.12.
• [x] Add workflow_dispatch trigger to GHA pytest-with-coverage workflow to enable workflow to be triggered from GitHub CLI, browser or via API
• [x] Drop Python 3.10 & 3.11 from GHA pytest-with-coverage workflow
• [x] Change setup.cfg python_requires to >=3.12
• [x] Change conda environment descriptions to use Python 3.12
  • [x] environment-dev.yaml
  • [x] environment-prod.yaml
  • [x] environment-rtd.yaml
• [x] Change sphinx-linkcheck workflow to Python 3.12
• [x] Change index doc & README to Python 3.12 for package development

[codecov[bot]]

Codecov Report

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

Project coverage is 74.83%. Comparing base (7e7aae8) to head (ac2aa71). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #77 +/- ## ======================================= Coverage 74.83% 74.83% ======================================= Files 14 14 Lines 906 906 Branches 87 161 +74 ======================================= Hits 678 678 Misses 221 221 Partials 7 7 ``` | [Flag](https://app.codecov.io/gh/SalishSeaCast/salishsea-site/pull/77/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SalishSeaCast) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/SalishSeaCast/salishsea-site/pull/77/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SalishSeaCast) | `74.83% <100.00%> (ø)` | | 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=SalishSeaCast#carryforward-flags-in-the-pull-request-comment) to find out more.

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