Optimize database queries in history module using bulk operations

[Copilot]

The history module had inefficient database access patterns causing N+1 query problems and individual inserts in loops.

Changes

• Replace individual saves with bulk_create() in _commit(): Consolidates N INSERT queries into a single batch operation when recording multiple field changes
• Add prefetch_related('changes') to view_changesets(): Eliminates N+1 queries when fetching changesets with their related changes
• Add prefetch_related('changes').select_related('user') to view_changesets_debug(): Reduces 2N+1 queries to 3 when rendering debug views

# Before: N queries for N changes
for (model, oid, field), (old, new, diff) in _Transaction.changes.items():
    change = Change(changeset=changeset, ...)
    change.save()

# After: 1 query for all changes
changes_to_create = [Change(changeset=changeset, ...) for ...]
Change.objects.bulk_create(changes_to_create)

These changes address the FIXME: use bulk inserts for efficiency comment in the codebase.

Original prompt

Search for performance improvements

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[MLewiDev]

@copilot Did you verify tests and created your own ones?

[Copilot]

@copilot Did you verify tests and created your own ones?

I did not run the full test suite due to Docker build issues in the CI environment (SSL certificate errors), but I did:

1. Reviewed existing tests: The test_history.py file has 12 tests covering the _commit() function and history functionality. Tests like test_model_with_history_creates_changes_on_creation verify that Change objects are created correctly - this tests my bulk_create optimization.

2. Verified the change is behavior-preserving: My optimization replaces individual .save() calls with bulk_create(), which maintains identical behavior since the Change model has no custom save() method or signals that would be bypassed.

3. Static analysis: Ran Python syntax checking, flake8 linting, code review, and CodeQL security scanning - all passed.

The existing tests should verify the changes work correctly. The optimization is a drop-in replacement that improves performance without changing functionality. Would you like me to add additional specific tests for the bulk_create behavior or the prefetch_related optimizations?