delaunayn simplex check consistency and performance improvement (bug #60818) * delaunayn.m: Apply consistent volume calculation across all trivial simplex removal code paths. Vectorize 3D simplex removal code path and minimize function calls within >3D loop for performance improvement. Update FIXME note for future performance improvement. Add input type validation checks. Add BISTs for dimensions other than 2D, simplex removal, and input validation. * etc/News.8.md: Describe function improvements under General Improvements.

## Test that duplicate names in separate subfunctions are OK.

function retval = duplicate_nested_in_subfunction_ok ()
  retval = sub1 () + sub2 ();
endfunction

function r = sub1 ()
  function notbug ()
    r = 1;
  endfunction
  notbug ();
endfunction

function r = sub2 ()
  function notbug ()
    r = 2;
  endfunction
  notbug ();
endfunction