Fix Invalidation issue when datachecker is changed

[datamik]

AB#314710

Summary
Editing DataChecker-related models in Django admin triggered post_save signals that bulk-invalidated every validated household and individual in every program using that checker. A single form save could fire many signals (parent + inlines), so the same programs were invalidated repeatedly.

Problem

• Saving DataChecker itself (e.g. name/description) ran full invalidation even though those fields do not affect validation rules.
• Saving Fieldset, FlexField, or DataCheckerFieldset via admin (often several .save() calls per submit) re-ran invalidation for the same programs on each signal.

Fix

• Signals — Stop listening to DataChecker post_save. Composition changes are still handled via DataCheckerFieldset (and related models).
• Admin — Override hope_flex_fields admins (DataChecker, Fieldset, FlexField) to wrap POST saves in collect_invalidations(), so all signals in one form submit defer invalidation and each program is processed once at the end. FieldsetAdmin.all_fields is wrapped the same way.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.93%. Comparing base (955bc7c) to head (11ada58).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #384   +/-   ##
========================================
  Coverage    96.92%   96.93%           
========================================
  Files          237      238    +1     
  Lines         9759     9783   +24     
  Branches      1081     1081           
========================================
+ Hits          9459     9483   +24     
  Misses         143      143           
  Partials       157      157           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[domdinicola]

@datamik resume