Add pytest-cmake CLI and remove deprecated CMake module integration docs

[buddly27]

• Added pytest-cmake command-line tool with --cmake-dir to print the CMake config path, simplifying integration for virtualenvs, non-standard installs, and --user installs.
• Updated documentation to recommend using the CLI instead of manually setting CMAKE_PREFIX_PATH.
• Removed documentation for integrating the CMake module directly from the Git repository, as this unsustainable method was already discouraged.
• Updated packaging configuration to include CLI entry point and adjust included files.

Closes #59