python 3.14 compatibility tests, drop python 3.7 from tests

[scottshambaugh]

The code in skyfield works and tests pass without changes when I build and run with python 3.14. This extends the python tests to include everything up through 3.14.

Other notes that make setting up testing easier:

• Python 3.7 is removed from the tests as it's EOL and no longer available through uv
• The test script grabs the last edited wheel for testing
• Grab the github for assay if it doesn't already exist locally

Note however that assay itself is not python 3.14 compatible due to a bytecode change, so the test currently fails. There is a minor fix that restores that, if you insert the following near the top of https://github.com/brandon-rhodes/assay/blob/master/assay/assertion.py:

# Python 3.14 replaced LOAD_ASSERTION_ERROR with LOAD_COMMON_CONSTANT
# AssertionError is always at index 0 in the common constants
if _python_version >= (3, 14):
    op.load_assertion_error = op.load_common_constant

@brandon-rhodes want me to open a PR in that repo? Not sure how much it's still active