Refactor benchmark utilities: centralize core logic into _run_benchmark_core (#3191)

Summary:
Pull Request resolved: #3191

Removed redundant logic in `benchmark` and `benchmark_func` by moving shared timing, memory, and profiling code into a new `_run_benchmark_core` function. Ensured the backward-compatibility.

Reviewed By: aliafzal

Differential Revision: D78290979

fbshipit-source-id: 4d5e117f890b6da36776f75962f1dc82ece710b7

Author: SSYernar