Use sccache to cache Windows release builds

[Gold856]

I heard you didn't have any DevOps people :) Ready to have your mind blown?

Windows CI:
https://github.com/borglab/gtsam/actions/runs/18232137161/job/51989459877
Uncached run takes ~1 hour, build takes ~50 minutes.

https://github.com/Gold856/gtsam/actions/runs/18301774268/job/52111040305
Completely cached run takes 10 minutes, build takes ~3 minutes. More time is spent installing dependencies than building code :)

Less fantastical is vcpkg:
https://github.com/borglab/gtsam/actions/runs/18228729434/job/51906606067
~1.5 hours to complete a Windows run, build takes 49 + 39 minutes.

https://github.com/Gold856/gtsam/actions/runs/18301774262/job/52111040326
Run takes ~22 minutes, build takes ~17 + ~2 minutes. Spent 14 minutes on building the Python modules (I believe these use LTO? I assume that's why it spends so long linking.)

And obviously, these are optimal runs, with 100% cache hit rates. Real usage will be much worse. For this project, I would expect build times should take 50% less time 99% of the time compared to before, given what's modified frequently. As long as you don't touch your base headers in base or geometry, I'd expect builds to take around 10-20 minutes, assuming a header in nonlinear, sfm, or slam was modified.

sccache uploaded ~680.8 MB in the GitHub Actions Cache. You should be able to comfortably have a dozen open PRs with no object files shared between them before you overflow your cache. If you want, we can probably cache one or two more builds and still have space left over for PRs (assuming complete cache misses.)

I also took the liberty to fix your vcpkg cache so a new one isn't saved if it's a 100% match. You're already using 9 GB and you not even using 95% of it! And I implemented a cache cleaner to clean up caches after PRs are closed to free up space for other PRs.
Resolves #2255.

[Copilot]

Pull Request Overview

This PR implements sccache to significantly reduce Windows CI build times from ~1 hour to ~10 minutes for cached builds. It also adds cache cleanup automation and fixes vcpkg cache efficiency.

• Adds sccache compiler caching to Windows builds for faster compilation
• Implements automatic cache cleanup after PR closure to manage storage
• Introduces optional precompiled headers support for MSVC builds

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
.github/workflows/build-windows.yml	Adds sccache setup and compiler launcher configuration for Release builds
.github/workflows/vcpkg.yml	Integrates sccache for Windows builds and prevents duplicate cache saves
.github/workflows/cache-cleanup.yml	New workflow to automatically clean up PR caches when closed
cmake/HandleGeneralOptions.cmake	Adds MSVC precompiled headers build option
cmake/HandlePrintConfiguration.cmake	Adds configuration printing for precompiled headers setting
cmake/GtsamAddPch.cmake	Makes precompiled headers conditional on the new build option

[dellaert]

This is amazing! I always lamented the windows build taking so long !

[dellaert]

Super-cool, merging now.