core/ci: fix windows-specific issues

- use portable separators
- paths should be prepended with r' (so backwards slash isn't treated as escaping)
- sqlite connections should be closed (otherwise windows fails to remove the underlying db file)
- workaround for emojis via PYTHONUTF8=1 test for now
- make ZipPath portable
- properly use tox python environment everywhere

  this was causing issues on Windows
  e.g.
      WARNING: test command found but not installed in testenv
        cmd: C:\hostedtoolcache\windows\Python\3.9.12\x64\python3.EXE

tests/commits.py

@@ -1,9 +1,14 @@
-# TODO need fdfind on CI?
 from pathlib import Path
 
 from more_itertools import bucket
 import pytest
 
+import os
+pytestmark = pytest.mark.skipif(
+    os.name == 'nt',
+    reason='TODO figure out how to install fd-find on Windows',
+)
+
 
 def test() -> None:
     from my.coding.commits import commits