Dropped support for Python 3.9 and test on 3.14

[agronholm]

Changes

This drops support for Python 3.9 and adds Python 3.14 to the tox configuration and GitHub CI matrix.

Checklist

If this is a user-facing code change, like a bugfix or a new feature, please ensure that
you've fulfilled the following conditions (where applicable):

• You've added tests (in tests/) which would fail without your patch
• You've added a new changelog entry (in CHANGES.rst).

If this is a trivial change, like a typo fix or a code reformatting, then you can ignore
these instructions.

Updating the changelog

If there are no entries after the last release, use **UNRELEASED** as the version.
If, say, your patch fixes issue #123, the entry should look like this:

- Fix big bad boo-boo in task groups
  (`#123 <https://github.com/agronholm/sqlacodegen/issues/123>`_; PR by @yourgithubaccount)

If there's no issue linked, just link to your pull request instead by updating the
changelog after you've created the PR.

[coveralls]

coverage: 97.632% (-0.1%) from 97.767%
when pulling e6f044b on py314
into 6ddf95c on master.