Add group affinity

[Alan-Jowett]

This pull request includes several changes to the usersim module, focusing on improving thread priority and affinity management. The changes involve replacing existing functions with new ones that cache thread priority and affinity to optimize performance.

Key Changes:

Thread Priority and Affinity Management:

• Replaced usersim_set_affinity_and_priority_override and usersim_clear_affinity_and_priority_override with usersim_set_current_thread_priority and usersim_set_current_thread_affinity functions to manage thread priority and affinity more efficiently by caching values. [1] [2]
• Introduced new thread-local variables to cache thread priority and affinity, replacing the previous override mechanism.
• Updated various functions to use the new usersim_set_current_thread_priority and usersim_set_current_thread_affinity functions, ensuring thread priority and affinity are set only when necessary. [1] [2] [3] [4] [5] [6]

Code Cleanup:

• Removed the old usersim_get_current_thread_group_affinity function and related affinity management functions that are no longer needed. [1] [2]

Tests:

• Updated tests to reflect the removal of the old affinity and priority override functions and to validate the new behavior. [1] [2] [3]