Abstract-tech: Fix: preserve ORA date_config_type through OLX export/import

[ronakpansuriya]

TL;DR - Fixes date_config_type (ORA schedule mode: manual / match subsection/match course end) silently resetting to "manual" whenever a course is exported and re-imported.

Issue: #2418

What changed?

• openassessment/xblock/utils/xml.py -- parse_from_xml() now reads the date_config_type attribute off the XML node (if present), validates it against the three known values (manual / subsection / course_end), and includes it in the returned config dict. Raises UpdateFromXmlError on an invalid value, same pattern as the other validated fields in this function.
• openassessment/xblock/utils/xml.py -- serialize_content_to_xml() now writes date_config_type onto the XML node when it's set, following the same if <field> is not None: pattern used for every other field here.
• openassessment/xblock/openassessmentblock.py -- parse_xml() now assigns date_config_type from the parsed config dict onto the block, falling back to DATE_CONFIG_MANUAL when the value is None (i.e. an old export from before this fix, or a course that never touched this setting). This fallback is intentional and important for backward compatibility: assigning None directly would mark the field as explicitly set to None in the XBlock field system instead of falling through to the class default, which would change behavior for every existing course that's never used this setting.
• Added TestDateConfigTypeXml to openassessment/xblock/test/test_xml.py -- covers reading a valid value, missing-attribute backward compatibility, invalid-value rejection, serialization, and a full parse -> serialize -> parse round trip.

Testing Instructions

Automated:

pytest openassessment/xblock/test/test_xml.py -v

182 passed, 0 failed (177 pre-existing + 5 new, all in TestDateConfigTypeXml).

Manual, to reproduce the original bug and confirm the fix:

1. Create a course, add an ORA to a unit.
2. Open the ORA's Schedule tab, select "Match deadlines to the subsection due date", save, publish.
3. Studio -> Tools -> Export Course, download the tarball.
4. Create a new, empty course. Studio -> Tools -> Import Course, upload the tarball from step 3.
5. Open the ORA in the new course, go to the Schedule tab.

Before this fix: reverts to "Configure deadlines manually" with placeholder dates (2001-01-01 / 2099-12-31).
After this fix: correctly shows "Match deadlines to the subsection due date" selected.

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[itsjeyd]

@ronakpansuriya Thank you for your contribution!

@openedx/axim-engineering Pinging you since this repo is currently unmaintained. Could you please enable tests for this PR?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.46%. Comparing base (95c188d) to head (ad795a3).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2420      +/-   ##
==========================================
+ Coverage   95.45%   95.46%   +0.01%     
==========================================
  Files         198      198              
  Lines       22755    22842      +87     
  Branches     1548     1551       +3     
==========================================
+ Hits        21720    21807      +87     
  Misses        780      780              
  Partials      255      255              

Flag	Coverage Δ
unittests	95.46% <100.00%> (+0.01%)	⬆️

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[e0d]

@ronakpansuriya I notice there are some commit-lint failures. Please note that we use conventional commits across Open edX projects. You can read about the details here. Can you please amend your commit messages to follow our standard?

[ronakpansuriya]

Hi @e0d thanks for the review! I've updated the commit message to follow the Conventional Commits format. Could you please re-run the tests/lint check and let me know if anything else is missing?