Confirm support for Python 3.14, drop 3.9

[khaeru]

Python 3.14 was released 2024-10-07. This PR is to:

• Check/confirm that message-ix-models is compatible with the new version by updating CI workflows.
  • Update the GitHub ruleset config to require 3.14 jobs to pass, instead of 3.13.
• Check/confirm the existence of compatible releases of upstream dependencies. If those releases are not immediately available, the PR can aid to monitor and track upstream issues.
  • Confirm support for Python 3.14 and drop 3.9 message_ix#985 and further upstream.
• Drop support for Python 3.9, which reached end-of-life (no more updates, even security updates) on 2025-10-07.
  • Remove any code marked as for Python 3.9 compatibility only. Depending on these changes, part or all of the functionality may remain usable with Python 3.9 if users have extreme need.
  • Make any general clean-ups or improvements possible with features available from Python 3.10.
    • Use the type union operator instead of typing.Optional and typing.Union. This is achieved by running ruff check --select F401,UP007,UP045 --fix or similar multiple times, plus some small manual clean-ups. See the ruff docs.
    • Use match/case instead of some if statements with multiple elif blocks. Too many instances in the code base to do in this PR, so not included.

How to review

For @glatterf42:

• Read the commit messges
• Note that the CI checks all pass.

Others notified as code owners:

• No review needed.
• Note the Python ≥3.10 semantics for type annotations, here, and use these in the future when updating these files.

PR checklist

• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• Add, expand, or update documentation.
• Update doc/whatsnew.

After approval:

• Rebase to drop the TEMPORARY commit(s).

[codecov]

Codecov Report

❌ Patch coverage is 99.17355% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.7%. Comparing base (0cf55ca) to head (3f52423).

Files with missing lines	Patch %	Lines
message_ix_models/model/water/data/demands.py	66.6%	1 Missing ⚠️
message_ix_models/tools/wb.py	50.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #443     +/-   ##
=======================================
- Coverage   75.3%   74.7%   -0.7%     
=======================================
  Files        270     270             
  Lines      22331   22312     -19     
=======================================
- Hits       16836   16676    -160     
- Misses      5495    5636    +141     

Files with missing lines	Coverage Δ
message_ix_models/model/build.py	100.0% <ø> (ø)
message_ix_models/model/buildings/__init__.py	25.2% <100.0%> (ø)
message_ix_models/model/config.py	93.1% <100.0%> (ø)
message_ix_models/model/emissions.py	98.7% <100.0%> (ø)
message_ix_models/model/macro.py	100.0% <100.0%> (ø)
message_ix_models/model/material/build.py	69.2% <100.0%> (+2.5%)	⬆️
message_ix_models/model/material/data_ammonia.py	94.2% <100.0%> (ø)
...ge_ix_models/model/material/data_other_industry.py	69.1% <100.0%> (ø)
message_ix_models/model/material/data_petro.py	80.2% <100.0%> (ø)
message_ix_models/model/material/data_util.py	75.9% <100.0%> (ø)
... and 80 more

... and 6 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[glatterf42]

Based on the commit messages and the passing tests, this looks good to me :)