Fix legacy VEmex build compatibility on modern MATLAB/CMake for macOS

[yasser508]

Fixes the VEmex build scripts for modern MATLAB/CMake, mainly to address issue #4 (Apple Silicon linker failure when building the MEX solver for runJohansenVE). There were enough related rough edges nearby that I bundled a few other things in.
Changes

Handle both old and new FindMatlab variable names
Use MATLAB's detected MEX extension when available, with fallbacks for Intel and Apple Silicon on macOS
Drop -pg profiling from the default build — it shouldn't have been on
Fix OpenMP linking for newer CMake versions
Fix a typo in the mex copy/remove step
Use the platform shared library suffix instead of hardcoding .so
Make the MATLAB wrapper symlink command safer
Clearer build instructions in the README

Notes
I don't have MATLAB here so this is all static inspection — no live build test. If someone has a native Apple Silicon + MATLAB setup, a quick smoke test would go a long way. That's the exact environment that started this.
Refs #4

[yasser508]

PR with some VEmex build script cleanup for newer MATLAB/CMake on macOS. My guess is the issue is in the build config, not runJohansenVE — outdated variable names, wrong MEX extension, macOS-specific naming, stale README. Touched all of those.
No MATLAB here so no real build test. If anyone has Apple Silicon + MATLAB, would love a quick sanity check.