Fix release versioning: keep tree ruff-clean, fail fast on dirty tag builds

The tagged v0.10.6 CI build produced wheels versioned
0.10.7.dev0+g503ce8e49.d20261004: setup.py was not ruff-format-clean, so
release.py's own 'ruff format .' step rewrote it, dirtying the checkout
before setuptools_scm ran. PyPI then rejected the local version segment
with HTTP 400.

- ruff-format setup.py
- release.py: on a v*-tagged HEAD, fail before building if the version
  is not a clean release, printing the dirty files
- add .gitattributes (eol=lf) so Windows checkouts can't dirty the tree
  via normalize_line_endings either

.gitattributes

@@ -0,0 +1 @@
+* text=auto eol=lf