CMake 4.5 makes `import std` available to every target that scans for
C++ modules and drops the experimental CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
gate and the CXX_MODULE_STD property. The module test no longer needs the
version-specific opt-in token, so the ci_module_cpp20 jobs no longer have
to pin CMake 4.3.4 and now request CMake ^4.5.0.
The modules, CMake and README documentation now list the CMake, generator
and toolchain requirements for building the module and for `import std;`.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann