Chore: Bump CMake, CI workflows

[marcizhu]

This PR bumps the minimum required CMake version from 3.1 to 3.31, the last supported version for CMake 3.x. It also updates the CI workflows and fixes some issues with code coverage:

• Drops Clang 11 from CI builds, as the compiler is quite old and apt wasn't finding it on the default repos
• Uses lcov instead of gcov for collecting coverage data, gcov wasn't working for some reason
• Uses the official codecov GitHub Action instead of the Codecov Uploader script, as it's newer and better supported

In general I think these changes should be pretty safe and should allow using the library on newer versions of CMake. Let me know if you want any changes!

[marcizhu]

Hey @kthohr! Would it be possible to get this PR merged? Do you want any changes? I have some dependencies that are failing to build due to CMake being unsupported.

Thanks in advance! 😄