[FR]: Integrated ctest and other project improvements

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.

Start by reading the project CMakeLists.txt files and ci.yaml to understand the current build and test paths. Try the reported python3 -m build plus pytest workflow and inspect how CTest could cover the native project. Done would require a decided scope covering standardized testing and the selected CMake or packaging improvements.