Unit testing of splined Jastrows near cutoffs distances needed

Following the discussion in #4828 , better unit tests are needed for the Jastrow functions that use splines. e.g. Testing just before, at, after the cutoff values. Unit test level is needed so that sanitizer runs will catch invalid accesses. Should entail only a few extra evaluations in the existing unit tests. Not testing here led to us missing an out of bounds issue in the code.