[MNT] CI test matrix with unix, windows, and all supported python versions (#604)

Extends the test matrix to windows, Mac, and unix; and python to 3.10 to
3.14.

Depends on #601
to ensure the tests actually run.

#601 should be merged first.

Author: fkiraly

.github/workflows/testing.yml

@@ -22,8 +22,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest]
-        python-version: ["3.10"]
+        os: [ubuntu-latest, windows-latest]  #macos-latest fails downloads, see #593
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
 
     steps:
       - uses: actions/checkout@v6