Handle CMake Policy in Each Function

[threeal]

This issue suggests setting CMake policies within the scope of a function if the function requires specific CMake policy behavior, removing the need to specify a minimum CMake version at the top of the Assertion.cmake module.

This change may fix some issues related to CMake policy when using the Assertion.cmake module. It may also allow CMake with a lower version to continue using the Assertion.cmake module while still supporting the latest features.