Attempt to speed up Windows CI

[Copilot]

Windows CI was repeatedly downloading the Bazel binary via Bazelisk, adding avoidable latency and making runs more sensitive to transient network/DNS failures. This change adds Bazel disk-cache and persists the cache between workflow runs while leaving existing Bazel behavior intact.

• What changed

  • Added a dedicated Bazelisk cache root in the Windows workflow job env:
    • BAZELISK_HOME: ${{ github.workspace }}\.bazel-cache\bazelisk
  • Added an actions/cache step to restore/save Bazelisk downloads using:
    • key: windows-bazelisk-cache-${{ runner.os }}-${{ hashFiles('.bazelversion') }}
    • restore key prefix by OS for partial reuse

• Why this keying strategy

  • .bazelversion invalidates cache when Bazel version changes.
  • OS scoping prevents cross-platform cache contamination.

env:
  BAZELISK_HOME: ${{ github.workspace }}\.bazel-cache\bazelisk

- name: Restore Bazelisk cache
  uses: actions/cache@v4
  with:
    path: ${{ env.BAZELISK_HOME }}
    key: windows-bazelisk-cache-${{ runner.os }}-${{ hashFiles('.bazelversion') }}
    restore-keys: |
      windows-bazelisk-cache-${{ runner.os }}-

Also changes the Windows CI test/build target scope and adds profile capture/analysis.

[Copilot]

Pull request overview

This PR updates the Windows CI workflow to reduce cold-start latency and improve reliability by reusing cached Bazel/Bazelisk artifacts across runs, while also reshaping the Windows CI build/test flow and collecting Bazel profiles for analysis.

Changes:

• Persist Bazelisk’s downloaded Bazel binaries across workflow runs via BAZELISK_HOME + actions/cache.
• Add a Bazel disk cache restore/save step and pass --disk_cache to fetch/test/build commands.
• Split Windows CI into fastbuild test coverage + a narrow --config=opt smoke build, and emit/upload a Bazel profile + analysis output.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
python/tests/ci_windows_cppopts_test.py	Updates assertions to match the new Windows CI command structure (fastbuild tests, limited opt build, profile emission, cache usage).
.github/workflows/ci_windows.yml	Adds Bazelisk + Bazel disk caching, adjusts Windows CI target scope and compilation modes, and captures/analyzes Bazel profiles.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[tameware]

@zzcgumn, the Windows CI was sometimes timing out at 20 minutes. I asked Copilot to try to make it faster. This is what it came up with, but I'm not certain it's faster! I can ask Copilot for additional speedups.

[zzcgumn]

Interesting idea but I suggest we leave for 3.2.0. I am thinking that we want to check if similar caching schemes can speed Linux and macOS CI runs too.

[tameware]

Postponed for now. Will consider for v3.2.