correlated_field.py: Raise errors for users

Instead of validating the input via `assert`s in user-accessible
functions, raise appropriate errors.
9 jobs for nifty6_cfm_usability in 9 minutes and 52 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build Docker
passed #978391
build_docker_from_cache

00:00:24

 
  Test
passed #978393
test_mpi

00:07:07

passed #978392
test_serial

00:07:31

82.0%
 
  Demo Runs
passed #978398
run_bernoulli

00:00:43

passed #978399
run_curve_fitting

00:00:41

passed #978395
run_getting_started_1

00:00:46

passed #978396
run_getting_started_2

00:01:13

passed #978397
run_getting_started_3

00:01:55

passed #978394
run_ipynb

00:01:42