Sets up pre- and post- method verification of _ge and _gej group elements. At the moment, this is concerned mainly with imposing a tighter limit (than the default) on the magnitudes of field elements x, y (,z).
Having guarantees about the magnitudes in input group elements can let us avoid some of the normalization calls needed at the start of several group addition methods, and perhaps e.g. use an alternative double algorithm. There may be a trade-off between the effort needed to get outputs to meet lower limits vs the benefits that provides to other methods.
