Convert profile.rst to deprecation stub

The pure Python profile module is deprecated in 3.15 and scheduled for removal
in 3.17. Users should migrate to profiling.tracing (or use the cProfile alias
which continues to work).

The page now focuses on helping existing users migrate: it shows the old vs new
import style, keeps the shared API reference since both modules have the same
interface, and preserves the calibration docs for anyone still using the pure
Python implementation during the transition period.

Author: pablogsal