Add workflow for nightly full test (#853)

This workflow does a plain TFQ build & test. It's scheduled to run every night. Its purpose is to guard against failures that might be missed when skipping the long-running tests or using caching to speed up the CI runs. Unlike the CI checks invoked on PRs and similar events, this workflow builds everything without caching and runs the full test suite, including "eternal" tests that take a long time to run.

Author: mhucka

.github/workflows/ci-nightly-build-test.yaml

@@ -0,0 +1,138 @@
+# Summary: TFQ nightly full build & test.
+#
+# This workflow compiles TFQ and runs all test cases, to verify everything
+# works. Unlike the CI checks invoked on PRs and similar events, this workflow
+# builds everything without caching and runs the full test suite, including
+# "eternal" tests that take a long time to run. It is meant to guard against
+# failures that might be missed when skipping the long-running tests or using
+# caching to speed up the CI runs.
+#
+# For efficiency, it checks if there have been any commits in the past 24 hrs
+# and does not proceed if there have been none.
+#
+# This workflow also can be invoked manually via the "Run workflow" button at
+# https://github.com/tensorflow/quantum/actions/workflows/ci-build-checks.yaml
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+name: CI nightly test
+run-name: Continuous integration nightly build & test
+
+on:
+  schedule:
+    - cron: "15 6 * * *"
+
+  workflow_dispatch:
+    inputs:
+      py_version:
+        description: "Python version:"
+        type: string
+        default: "3.10.15"
+
+      save_artifacts:
+        description: Make Bazel artifacts downloadable
+        type: boolean
+        default: true
+
+env:
+  # Default Python version to use.
+  py_version: "3.10.15"
+
+  # Additional .bazelrc options to use.
+  bazelrc_additions: |
+    common --announce_rc
+    build --subcommands
+    build --auto_output_filter=none
+    build --show_progress_rate_limit=1
+    build --verbose_failures
+    test --test_output=errors
+    test --test_summary=detailed
+    test --test_timeout=6000
+    test --test_verbose_timeout_warnings
+
+concurrency:
+  # Cancel any previously-started but still active runs on the same branch.
+  cancel-in-progress: true
+  group: ${{github.workflow}}-${{github.event.pull_request.number||github.ref}}
+
+jobs:
+  Decision:
+    runs-on: ubuntu-24.04
+    outputs:
+      run: ${{steps.commits.outputs.count > 0}}
+    steps:
+      - name: Check out a sparse copy of the git repo for TFQ
+        uses: actions/checkout@v4
+        with:
+          sparse-checkout: .
+
+      - name: Get number of commits in the last 24 hrs
+        id: commits
+        run: |
+          set -x
+          count=$(git log --oneline --since '24 hours ago' | wc -l)
+          echo "count=$count" >> "$GITHUB_OUTPUT"
+
+  Nightly:
+    if: needs.Decision.outputs.run == 'true'
+    name: Build and test
+    needs: Decision
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Check out a copy of the TFQ git repository
+        uses: actions/checkout@v4
+
+      - name: Set up Python ${{inputs.py_version || env.py_version}}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{inputs.py_version || env.py_version}}
+
+      - name: Set up Bazel
+        uses: bazel-contrib/setup-bazel@0.9.1
+        with:
+          bazelrc: ${{env.bazelrc_additions}}
+
+      - name: Build wheel
+        run: |
+          set -x
+          pip install --upgrade pip setuptools wheel
+          # The next script does a pip install, configure, & bazel build.
+          ./scripts/build_pip_package_test.sh
+
+      - name: Test wheel
+        run: |
+          set -x
+          ./scripts/run_example.sh
+
+      - name: Test rest of TFQ
+        run: |
+          set -x -o pipefail
+          ./scripts/test_all.sh 2>&1 | tee test_all.log
+
+      - name: Test tutorials
+        run: |
+          set -x -o pipefail
+          pip install jupyter
+          pip install nbclient==0.6.5 jupyter-client==6.1.12 ipython==7.22.0
+          pip install ipykernel==5.1.1
+          pip install gym==0.24.1
+          pip install seaborn==0.12.0
+          pip install -q git+https://github.com/tensorflow/docs
+          cd ..
+          python quantum/scripts/test_tutorials.py 2>&1 | \
+            tee quantum/test_tutorials.log
+
+      - if: failure() || inputs.save_artifacts == 'true'
+        name: Make artifacts downloadable
+        uses: actions/upload-artifact@v4
+        with:
+          name: test-artifacts
+          retention-days: 7
+          include-hidden-files: true
+          path: |
+            test_all.log
+            test_tutorials.log
+            /home/runner/.bazel/execroot/__main__/bazel-out/
+            !/home/runner/.bazel/execroot/__main__/bazel-out/**/*.so
+            !/home/runner/.bazel/execroot/__main__/bazel-out/**/*.o
+            !/home/runner/.bazel/execroot/__main__/bazel-out/**/_objs
+            !/home/runner/.bazel/execroot/__main__/bazel-out/**/_solib_k8