Add fillval option to gwcs_blot

[melanieclarke]

Currently the gwcs_blot function always fills missing data with 0.0. JWST data uses NaN as the missing value filler for resample by default, so it would be nice to be able to set NaN as the missing value for blotted images too. This PR just adds the option, defaulting to the existing value of 0.0.

Tasks

• update or add relevant tests
• update relevant docstrings and / or docs/ page
• Does this PR change any API used downstream? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see below for change types)
  • run regression tests with this branch installed ("git+https://github.com/<fork>/stcal@<branch>")
    • jwst regression test
    • romancal regression test

news fragment change types...

• changes/<PR#>.apichange.rst: change to public API
• changes/<PR#>.bugfix.rst: fixes an issue
• changes/<PR#>.general.rst: infrastructure or miscellaneous change

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.76%. Comparing base (3b924fb) to head (8988d2c).
Report is 70 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #291      +/-   ##
==========================================
+ Coverage   84.74%   84.76%   +0.02%     
==========================================
  Files          44       44              
  Lines        8527     8542      +15     
==========================================
+ Hits         7226     7241      +15     
  Misses       1301     1301              

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[braingram]

Thanks! LGTM.

[emolter]

LGTM too

[melanieclarke]

This is internal to stcal, not yet used elsewhere, so I will go ahead and merge.