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.

%!function rval = sggval (val)
%!  global gval
%!  if (nargin == 1)
%!    gval = val;
%!  else
%!    rval = gval;
%!  endif
%!endfunction

%!test <*53599>
%! global gval
%! assert (isempty (gval))
%! sggval (13);
%! assert (sggval (), 13);
%! assert (gval, 13);
%! clear global gval
%! assert (sggval (), [])
%! gval = 42;
%! assert (sggval (), []);
%! clear gval
%! global gval
%! gval = 42;
%! assert (sggval (), 42);
%! clear -global gval;  # cleanup after test