update CMake threads behavior

See: https://cmake.org/cmake/help/latest/module/FindThreads.html

We should make a few small updates to modernize the CMake threads behavior:

1. We should use the `Threads::Threads` target vs. `${CMAKE_THREAD_LIBS_INIT}`.
2. We should investigate whether we should set `THREADS_PREFER_PTHREAD_FLAG` to `TRUE`.

Start with the repository's CMake build configuration and read the linked FindThreads documentation. Locate uses of CMAKE_THREAD_LIBS_INIT, compare them with the Threads::Threads target, and investigate whether THREADS_PREFER_PTHREAD_FLAG should be enabled. Done means the modernized behavior is applied consistently and the project still configures and builds successfully.

Written by the indexing model from the issue text.