Make explicit the location for the `CMakeUserPresets.json` file.
Update docs tests documentation.
Move `BUILD_DIR` and `PROGRAM_PREFIX` comments into the functional tests todo.
Add cmake to MacPorts/FreeBSD install instructions.
Add ccache to example `CMakeUserPresets.json` (it isn't otherwise documented, and is no longer as obvious without an `ENABLE_CCACHE` makevar).
Addressing comments
- add `uv` to dependencies: saves builder(s) from manually having to manage a venv for python build dependencies
- when building wheels, pip automatically creates the environment with those dependencies, so no need for uv
- when running simply `make ENABLE_PYOSYS=1`, this is not the case. people attempting to `pip3 install --upgrade pybind11 cxxheaderparser` to add it to their system packages will be met with a scare message about "breaking system packages"
- update installation instructions to drop boost and add uv instead
- update ci scripts to use `macos-15[-intel]` (`macos-13` sunset in early december)
