ci: build Python wheel once per OS, test across Python versions

Split the Python CI workflow into build and test phases. The build
job compiles the abi3 wheel once per OS, then test jobs download
and install it across Python 3.10-3.13. This avoids redundant Rust
compilation — particularly on Windows where builds take ~30 min each.

Also removes path filters so Python tests run on all repo changes,
since the build overhead is now minimal.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: cpsievert

.github/workflows/python.yml

@@ -2,24 +2,21 @@ name: Python
 
 on:
   push:
-    paths: ['ggsql-python/**', '.github/workflows/python.yml']
   pull_request:
-    paths: ['ggsql-python/**', '.github/workflows/python.yml']
 
 jobs:
-  test:
+  build:
     strategy:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python: ['3.10', '3.11', '3.12', '3.13']
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
 
       - uses: actions/setup-python@v5
         with:
-          python-version: ${{ matrix.python }}
+          python-version: '3.10'
 
       - uses: actions/setup-node@v4
         with:
@@ -45,10 +42,37 @@ jobs:
           args: --release
           sccache: true
 
+      - name: Upload wheel
+        uses: actions/upload-artifact@v4
+        with:
+          name: wheel-${{ matrix.os }}
+          path: target/wheels/ggsql-*.whl
+
+  test:
+    needs: build
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        python: ['3.10', '3.11', '3.12', '3.13']
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python }}
+
+      - name: Download wheel
+        uses: actions/download-artifact@v4
+        with:
+          name: wheel-${{ matrix.os }}
+          path: dist
+
       - name: Install wheel and test dependencies
         shell: bash
         run: |
-          WHEEL=$(ls target/wheels/ggsql-*.whl)
+          WHEEL=$(ls dist/ggsql-*.whl)
           pip install "${WHEEL}[test]"
 
       - name: Run tests