Fix wheel test import and run on all pushes

[espg]

Earlier we were limiting our build matrix to cut down on CI/CD run time-- this isn't needed anymore given the version 0.6.0 refactor, which significantly streamlines our dependencies.

Summary

• Fix test-wheels job to run pytest from /tmp so Python imports the installed wheel from site-packages, not the local source tree (which lacks the compiled _rustie extension)
• Remove tag-only gate (if: startsWith(github.ref, 'refs/tags/')) so test-wheels runs on every push to main and PR, surfacing failures before release time

Context

The test-wheels job has been silently broken — it checked out the source tree, installed the wheel, then ran pytest mortie/tests/... which resolved import mortie to the local source directory (no _rustie.abi3.so) instead of
the installed wheel. This only manifested when pushing the 0.6.0 tag because test-wheels was gated to tag pushes only.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.49%. Comparing base (184f1fd) to head (7de05fb).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #18   +/-   ##
=======================================
  Coverage   86.49%   86.49%           
=======================================
  Files          13       13           
  Lines        1770     1770           
=======================================
  Hits         1531     1531           
  Misses        239      239           

Flag	Coverage Δ
unittests	86.49% <ø> (ø)

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[codspeed-hq]

Merging this PR will not alter performance

✅ 14 untouched benchmarks

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_{Comparing fix/wheel-test-import (7de05fb) with main (184f1fd)¹}

Footnotes

1. No successful run was found on main (4e75d1c) during the generation of this report, so 184f1fd was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩