Fix spec class attribute for PersistenceStep and RefPixStep

[jdavies-st]

This PR fixes the comments in JumpStep.spec which were missing # before the comment.

PersistenceStep.spec comments were also not formatted correctly and too long.

RefPixStep.spec comments were completely missing. Pulled summaries of these from the docs.

Now all steps produce proper output when one does:

$ strun step_alias --help

Also a small change in assign_wcs picked up by the style checker

check-style: commands[0]> ruff .
jwst/assign_wcs/nirspec.py:404:8: E721 Do not compare types, use `isinstance()`
jwst/assign_wcs/nirspec.py:1828:8: E721 Do not compare types, use `isinstance()`

Checklist for maintainers

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• Make sure the JIRA ticket is resolved properly

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (c86ff0e) 76.54% compared to head (2c8b50c) 76.54%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7803   +/-   ##
=======================================
  Coverage   76.54%   76.54%           
=======================================
  Files         456      456           
  Lines       36947    36947           
=======================================
  Hits        28282    28282           
  Misses       8665     8665           

Flag	Coverage Δ		*Carryforward flag
nightly	77.39% <ø> (ø)		Carriedforward from 6707e76

*This pull request uses carry forward flags. Click here to find out more.

Files Changed	Coverage Δ
jwst/persistence/persistence_step.py	67.79% <ø> (ø)
jwst/refpix/refpix_step.py	73.17% <ø> (ø)

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[hbushouse]

LGTM