[FR]: Integrated ctest and other project improvements

[LecrisUT]

Problem description

When trying to work on https://github.com/pybind/pybind11/pull/5094, I have encountered a few issues:

• The project does not use ctest. This makes it quite hard for packagers to find and run tests. In principle it should use ctest --build-and-test to test native CMake projects. For some inspiration, here is a template I have.
• Building and testing from sdist is not possible, i.e.: python3 -m build + pytest
• Usage of custom Find<Package>.cmake when there are upstream packaging available with good CMake support: catch, eigen3
• In general, the CMake project can be improved among a few things: inverting the version detection to be defined in CMake, making the CMakeLists.txt files more readable

I am using the ci.yaml to fill in the gaps about how to the testing, but it would be much appreciated if the project can use standardized tools.