Update cmake_minimum_required version

As of CMake@4.0, compatibility with CMake < 3.10 is deprecated

Since we have 3.8 listed in several places across blt as the `cmake_minimum_required` version, we should increase this beyond 3.10.

Search the repository for cmake_minimum_required and the listed 3.8 version; no specific files or tests are named in the issue. Check the affected CMake configurations, update every relevant minimum version beyond 3.10, and verify that the project still configures and its existing tests pass.

Written by the indexing model from the issue text.