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

my/config.py

@@ -19,7 +19,7 @@ from my.core import Paths, PathIsh
 class hypothesis:
     # expects outputs from https://github.com/karlicoss/hypexport
     # (it's just the standard Hypothes.is export format)
-    export_path: Paths = '/path/to/hypothesis/data'
+    export_path: Paths = r'/path/to/hypothesis/data'
 
 class instapaper:
     export_path: Paths = ''