Build system modernization

[zayenz]

This PR overhauls the whole Gecode build system. It has the following large changes

• Removed the contribs directory. Simplifies building and build systems, and has not been used for a long time.
• CMake is separated from autoconf, updated, and requires version 3.21
• Autoconf is modernized, and without contribs the configure.ac.in is no longer needed
• Switched from Perl to Python using uv for all scripts
• A full test-matrix that compiles on Linux, Mac, and Windows on GitHub.

A new requirement for building is to have uv installed. This simplifies the external dependencies from a system installed Perl or Python to a single dependency that will manage an isolated virtual environment for each script.