chore: attempt to speed up tests

Author: parthea

.github/workflows/unittest.yml

@@ -41,6 +41,17 @@ jobs:
     - name: Install nox
       run: |
         uv pip install --system nox nox-uv
+    # Caches compiled wheels locally to prevent building heavy libraries
+    # such as grpcio, which we build from scratch on every run for Python 3.15+.
+    # Follow https://github.com/grpc/grpc/issues/41010 for updates.
+    - name: Cache Built Python 3.15 Wheels
+      if: matrix.python == '3.15'
+      uses: actions/cache@v4
+      with:
+        path: .uv-wheel-cache
+        key: ${{ runner.os }}-uv-wheels-3.15-${{ hashFiles('packages/**/testing/constraints*.txt') }}
+        restore-keys: |
+          ${{ runner.os }}-uv-wheels-3.15-
     - name: Run unit tests
       env:
         COVERAGE_FILE: ${{ github.workspace }}/.coverage-${{ matrix.python }}
@@ -58,6 +69,8 @@ jobs:
         if [ "${{ matrix.python }}" = "3.15" ]; then
           export NOX_FORCE_VENV_BACKEND="venv"
           export VIRTUALENV_SEEDER=""
+          # Route uv cache to our persistent workspace directory
+          export UV_CACHE_DIR="${{ github.workspace }}/.uv-wheel-cache"
         fi
         ci/run_conditional_tests.sh
     - name: Upload coverage results