Remove memmap option

[emolter]

Closes #506

This PR hard-codes memmap to False when reading FITS and ASDF, and emits a warning when a user attempts to use memory mapping.

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 jwst regression tests with this branch installed ("git+https://github.com/<fork>/stdatamodels@<branch>")

news fragment change types...

• changes/<PR#>.feature.rst: new feature
• changes/<PR#>.bugfix.rst: fixes an issue
• changes/<PR#>.doc.rst: documentation change
• changes/<PR#>.removal.rst: deprecation or removal of public API
• changes/<PR#>.misc.rst: infrastructure or miscellaneous change

[emolter]

JWST regression tests started here https://github.com/spacetelescope/RegressionTests/actions/runs/15881902672

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.07%. Comparing base (d65ce14) to head (c817ddb).
⚠️ Report is 175 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #507      +/-   ##
==========================================
+ Coverage   81.02%   81.07%   +0.04%     
==========================================
  Files         110      110              
  Lines        5422     5431       +9     
==========================================
+ Hits         4393     4403      +10     
+ Misses       1029     1028       -1     

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[emolter]

@drlaw1558 How do these deprecation messages look to you?

[drlaw1558]

LG2M

[emolter]

This PR needs to wait until spacetelescope/jwst#9593 is merged; otherwise the warnings are emitted whenever a ModelContainer is initialized

[emolter]

spacetelescope/jwst#9593 is merged, rerunning regtests here: https://github.com/spacetelescope/RegressionTests/actions/runs/16123598864

[melanieclarke]

Looks good, pending clean regtests.

Did this one have an associated JP ticket? I know we asked INS if it was okay to remove the argument, did we hear a final word on that?

[emolter]

It did not have an associated ticket. David did bring it up in a JP coordination meeting and then subsequently gave me the go-ahead after hearing that nobody knew memmap was even an option - at least, that's how I interpreted it.

[emolter]

regtests are clean

[melanieclarke]

LGTM, but I'll hold off on approval to see if @braingram wants to review/comment.

[braingram]

Let's make the next version of stdatamodels 4.0.0 since this is a breaking change.