fix(ci): restore vcpkg binary caching

[acgetchell]

Replace the removed x-gha backend with a supported filesystem cache persisted through GitHub Actions. Share the setup across CI, sanitizers, coverage, and CodeQL while caching source downloads separately.

Summary by CodeRabbit

• CI Improvements

  • Added shared dependency caching across build, sanitizer, coverage, and code analysis workflows.
  • Improved build setup consistency across GCC, Clang, AppleClang, and MSVC environments.
  • Added compiler-specific cache handling to speed up repeated builds.

• Documentation

  • Updated maintenance documentation to describe the cached dependency setup used by CI.

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ℹ️ Recent review info

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Run ID: 2affadda-fe91-4e06-86bb-85f8bc8e0146

📥 Commits

Reviewing files that changed from the base of the PR and between 02682e8 and 2b27462.

📒 Files selected for processing (6)

• .github/actions/setup-vcpkg/action.yml
• .github/workflows/_sanitizer.yml
• .github/workflows/ci.yml
• .github/workflows/codecov-upload.yml
• .github/workflows/codeql.yml
• README.md

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Walkthrough

The PR adds a composite action for pinned vcpkg setup and cache restoration. CI workflows now use compiler-specific binary caches and the local action. The README documents the new setup and cache behavior.

Changes

Cached vcpkg CI

Layer / File(s)	Summary
Create cached vcpkg action .github/actions/setup-vcpkg/action.yml	Adds required cache-key and optional vcpkg-directory inputs. The action prepares vcpkg and restores binary and source caches.
Adopt cached setup in workflows .github/workflows/_sanitizer.yml, .github/workflows/ci.yml, .github/workflows/codecov-upload.yml, .github/workflows/codeql.yml	Configures writable vcpkg binary caches. Replaces direct lukka/run-vcpkg setup with the local action and compiler-specific cache keys.
Document cached vcpkg setup README.md	Documents manifest-based checkout selection, compiler-specific binary archives, separate source archives, and retained bootstrap validation.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• acgetchell/CDT-plusplus#99: Also changes GitHub Actions vcpkg setup and lukka/run-vcpkg usage.

Suggested labels: vcpkg_package_manager

Poem

Pinned tools align,
Caches flow through every build,
Compilers keep keys,
Sources rest apart from bins,
CI moves with less setup.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: restoring vcpkg binary caching in CI.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci/vcpkg-binary-cache

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[acgetchell]

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