Overhaul CI to improve resilance and efficiency

Add caching for pip and poetry downloads to reduce runtime
Add pinned pip version
Add poetry installation of local project
Remove bare pip install for local project installation

.github/workflows/ci.yaml

@@ -20,24 +20,51 @@ jobs:
           - version: 3.9
             toxenv: py39
     steps:
-      - uses: actions/checkout@v2
-      - name: Set up Python ${{ matrix.python.version }}
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup:python${{ matrix.python.version }}
         uses: actions/setup-python@v1
         with:
           python-version: ${{ matrix.python.version }}
-      - name: Install project
-        run: pip install .
-      - name: Run tests via ${{ matrix.python.toxenv }}
-        run: tox -e ${{ matrix.python.toxenv }}
+      - name: Setup:cache
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~/.cache/pip
+            ~/.cache/pypoetry/cache
+            ~/.poetry
+          # Including the hashed poetry.lock in the cache slug ensures that the cache
+          # will be invalidated, and thus all packages will be redownloaded, if the
+          # lockfile is updated
+          key: ${{ runner.os }}-${{ matrix.python.toxenv }}-${{ hashFiles('**/poetry.lock') }}
+      - name: Setup:env
+        run: .github/scripts/setup-env.sh
+      - name: Run:${{ matrix.python.toxenv }}
+        run: $HOME/ci/bin/tox -e ${{ matrix.python.toxenv }}
   Check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - name: Set up Python 3.8
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup:python3.8
         uses: actions/setup-python@v1
         with:
           python-version: 3.8
-      - name: Install project
-        run: pip install .
-      - name: Run meta checks
-        run: tox -e static -e static-tests -e security
+      - name: Setup:cache
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~/.cache/pip
+            ~/.cache/pypoetry/cache
+            ~/.poetry
+          # Hardcoded 'py38' slug here lets this cache piggyback on the 'py38' cache
+          # that is generated for the tests above
+          key: ${{ runner.os }}-py38-${{ hashFiles('**/poetry.lock') }}
+      - name: Setup:env
+        run: .github/scripts/setup-env.sh
+      - name: Run:static
+        run: $HOME/ci/bin/tox -e static
+      - name: Run:static-tests
+        run: $HOME/ci/bin/tox -e static-tests
+      - name: Run:security
+        run: $HOME/ci/bin/tox -e security