wfss_contam use datamodel in with context

[braingram]

When the DataModel is cleaned up (del is called) during garbage collection it will close any opened hdulists. This will make any subsequent attempts to load data from the hdulist fail (with ValueError: I/O operation on closed file).

DataModel prior to the below PR contained a self reference which created a reference cycle which made python fail to collect the object during generation 0 passes with the garbage collector. This meant that the hdulist was not immediately closed when the model fell out of scope.

Code in wfss_contam relied on this persistance as the model created in the following line is no longer referenced on subsequent lines.

dimage = datamodels.open(dir_image_name).data

python will attempt to clean up the opened data model and fail, keeping the hdulist (stored at dir_image_name) open. This allowed later lines that reference dimage to load the array data within the hdulist.

Fixing the reference cycle in stdatamodels in this PR: spacetelescope/stdatamodels#109 makes the datamodel more easily garbage collected which causes wfss_contam to fail due to the hdulist closing when the model is collected.

To keep the model in scope, the above line is replaced with a with context to make it explicit that the datamodel is held open which it's contents are read.

This is work towards fixing JP-2798.

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

[braingram]

Regression tests running here: https://plwishmaster.stsci.edu:8081/job/RT/job/JWST-Developers-Pull-Requests/525/

[codecov]

Codecov Report

Base: 78.61% // Head: 78.61% // No change to project coverage 👍

Coverage data is based on head (d89abc0) compared to base (d89abc0).
Patch has no changes to coverable lines.

❗ Current head d89abc0 differs from pull request most recent head e792de1. Consider uploading reports for the commit e792de1 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7425   +/-   ##
=======================================
  Coverage   78.61%   78.61%           
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  Files         455      455           
  Lines       39143    39143           
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  Hits        30772    30772           
  Misses       8371     8371           

Flag	Coverage Δ
nightly	78.61% <0.00%> (ø)
unit	51.34% <0.00%> (ø)

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[hbushouse]

Code looks good, as do all the CI and regtest results. But I would like it to have a change log entry (in CHANGES.rst). It's not a change in functionality or results, but enough of a change in the code that I'd like to have a record of it (as a bug fix).