fakeDec is too close to the pole; please add a utility to calculate "ra,dec" from pfsNominal

The current values in pfsDesignUtils.py are fakeRa, fakeDec = 100, -89.99, but that value is too close to the pole to do something simple such as

ra =  fakeRa  + pfiNominal[:, 0]/3600
dec = fakeDec + pfiNominal[:, 1]/3600

as that results in unphysical declinations. If you scale the nominal positions by such a small number that they don't have this problem, they are too close to each other to have distinct SHAs (as the pfsDesignId rounds to 1 arc second).

Please fix this, and add a utility routine to generate usable (fake!) (ra, dec) values from pfi positions. N.b. the current code doesn't check that the provided coordinates are consistent with the boresight; this routine would circumvent that problem, but we should check.