CMake 4.0+ support

CMake 4.0 [dropped](https://cmake.org/cmake/help/latest/release/4.0.html#deprecated-and-removed-features) compatibility with CMake 3.4 and older, which means that `cmake_minimum_required` and `cmake_policy` commands are affected. At the moment there are at least a couple of third-party libraries that want 3.0 and 2.8.x policies, so it's not possible to build the project using CMake 4.0 or newer.

No file or test is named. Start by locating the project's cmake_minimum_required and cmake_policy commands, then configure the project with CMake 4.0 or newer and identify third-party libraries that still request older policies. Done means configuration and the affected build complete successfully with CMake 4+.

Written by the indexing model from the issue text.