Test the sdist: pip install, verify labextension, pytests

caveat: a ~/.cargo/config.toml file is created when testing the
sdist which patches the perspective-python build so that it uses
perspective-server and perspective-client from the local git checkout.
This is so we can test unreleased changes to those crates together.

End users who download sdist artifacts produced in CI between releases
may find they don't build or work correctly, since those sdists will
contain dependencies on release versions of perspective-server and
perspective-client published to crates.io.

Signed-off-by: Tom Jakubowski <tom@prospective.dev>

.github/workflows/build.yaml

@@ -436,7 +436,7 @@ jobs:
     # /` |     |    /|
     # `--'     '   `-'
     #
-    build_and_test_juptyerlab:
+    build_and_test_jupyterlab:
         needs: [build_js, build_python]
         runs-on: ${{ matrix.os }}
         strategy:
@@ -646,6 +646,68 @@ jobs:
                   PACKAGE: "perspective-python"
                   # PSP_USE_CCACHE: 1
 
+    test_python_sdist:
+        needs: [build_and_test_jupyterlab]
+        runs-on: ${{ matrix.os }}
+        strategy:
+            fail-fast: false
+            matrix:
+                os:
+                    - ubuntu-22.04
+                arch:
+                    - x86_64
+                python-version:
+                    - 3.9
+        steps:
+            - name: Checkout
+              uses: actions/checkout@v4
+
+            - name: Config
+              id: config-step
+              uses: ./.github/actions/config
+
+            - name: Initialize Build
+              uses: ./.github/actions/install-deps
+              with:
+                  rust: "true"
+                  cpp: "true"
+                  python: "true"
+                  javascript: "false"
+                  skip_cache: ${{ steps.config-step.outputs.SKIP_CACHE }}
+
+            - uses: actions/download-artifact@v4
+              with:
+                  name: perspective-metadata
+
+            - uses: actions/download-artifact@v4
+              with:
+                  name: perspective-python-sdist
+
+            - name: Set up global perspective-server and perspective-client path overrides
+              # this makes it so the sdist is tested against unreleased changes
+              # made to perspective-client and perspective-server
+              run: |
+                  mkdir -p $HOME/.cargo
+                  cat > $HOME/.cargo/config.toml <<EOF
+                  [patch.crates-io]
+                  perspective-client = { path = "$PWD/rust/perspective-client" }
+                  perspective-server = { path = "$PWD/rust/perspective-server" }
+                  EOF
+
+            - name: Install perspective-python sdist
+              run: python -m pip install -vv ./perspective*.tar.gz
+
+            - name: Verify labextension
+              run: |
+                  jupyter labextension list --debug
+                  jupyter labextension list 2>&1 | grep '@finos/perspective-jupyterlab'
+
+            - name: Run import test
+              run: python -c 'import perspective'
+
+            - name: Run pytests
+              run: pytest -v --pyargs 'perspective.tests'
+
     # ,-,---.             .                 .
     #  '|___/ ,-. ,-. ,-. |-. ,-,-. ,-. ,-. | ,
     #  ,|   \ |-' | | |   | | | | | ,-| |   |<
@@ -765,7 +827,7 @@ jobs:
     publish:
         needs:
             [
-                build_and_test_juptyerlab,
+                build_and_test_jupyterlab,
                 test_python,
                 test_js,
                 benchmark_js,