Improve DAS conversions, coverage, and release workflow

[d-chambers]

Summary

This PR improves DASCore, DASPy, and XDAS interoperability, expands conversion test coverage across DASCore examples, and updates packaging/release automation for Python 3.12+.

What Changed

• Fixed BaseDAS -> daspy.Section conversion to preserve DASPy channel/time data order.
• Added generic coordinate get_start() and get_step() accessors for conversion code.
• Added DASPy support for evenly sampled ArrayCoordinate inputs.
• Added clearer rejection for DASPy-incompatible relative/numeric time axes.
• Added XDAS conversion support for ArrayCoordinate via dense coordinates.
• Preserved coordinate dimensions when converting to XDAS, including auxiliary coordinates such as latitude, longitude, x, y, and z.
• Fixed DASCore round-trip handling for ArrayCoordinate.
• Switched packaging from Hatchling to Setuptools dynamic versioning from unidas.__version__.
• Bumped minimum Python version to >=3.12.
• Updated CI to test Python 3.12, 3.13, and 3.14.
• Updated the release workflow to publish only when __version__ changes, then create a tag and GitHub release.
• Updated README installation guidance and DASPy compatibility notes.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (64e20ba) to head (9bea408).

Additional details and impacted files

@@             Coverage Diff             @@
##             main        #9      +/-   ##
===========================================
+ Coverage   93.61%   100.00%   +6.38%     
===========================================
  Files           1         1              
  Lines         313       338      +25     
===========================================
+ Hits          293       338      +45     
+ Misses         20         0      -20     

Flag	Coverage Δ
unittests	100.00% <100.00%> (+6.38%)	⬆️

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