Pull lib3mf from VCPKG

[vijaiaeroastro]

This PR updates colorscad to use lib3mf from vcpkg (see 3MFConsortium/lib3mf#424). I’ve verified that tests pass on all supported platforms.

Dependency update
colorscad was using a very old lib3mf. I initially upgraded to 2.4.1, but the existing test .3mf files do not include newer specs (2.4.1 adds trianglesets and volumetric/implicit specs) and the tests will fail otherwise. To maintain compatibility, this PR pins lib3mf to 2.3.2 in vcpkg.json.

Future upgrade
I recommend regenerating the test .3mf files with lib3mf 2.4.1 to take advantage of the new features. The next lib3mf release will include a static library, so upgrading then will simply require bumping the version in vcpkg.json (and a minor CI tweak).

Please review and merge if this meets your needs.

[jschobben]

This is great, thanks for this PR.
I'm new to VCPKG still, but not sure we can fully replace the usage of pkgconfig/fetchcontent. I'd like to use a preinstalled version of lib3mf when available (that might also be a requirement from Fedora, which has both lib3mf and colorscad packaged).
As for fetchcontent, I need to support exotic platforms (Termux on Android because I use that myself); I wasn't able to get vcpkg working there out-of-the-box with this PR's changes + a submodule fetch, it's also not a supported triplet so that's probably not a surprise.
Maybe VCPKG can be added to the existing setup; first try locating lib3mf via pkgconfig, if that fails use VCPKG, with ultimate fallback fetchcontent.