test: add edge case tests for view pager boundary check - #7

PR summary

Adds edge case unit tests for pagination covering the real _ViewBasePageIterator.check_boundary logic, which was previously only exercised via mocked boundary functions in test_pagination_key.py. New TestViewPagerBoundary class (using a real POST_VIEW pager via Pagination.new_pagination):

• test_boundary_identical_key_and_id_raises: a page boundary with identical view keys AND document IDs raises Cannot paginate on a boundary containing identical keys ... and document IDs ... on the next page request.
• test_boundary_identical_key_different_id_paginates: identical keys with different doc IDs paginate correctly, resuming with start_key/start_key_doc_id boundary options.

PR Checklist

Please make sure that your PR fulfills the following requirements:

• The commit message follows the
  Angular Commit Message Guidelines.
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• New tests
• Build/CI related changes
• Documentation content changes
• Other (please describe)

What is the current behavior?

The view pager duplicate-boundary error path (check_boundary in _ViewBasePageIterator) is not covered by any unit test; existing key pager tests use a mocked boundary function.

What is the new behavior?

No behavior change — test-only. Both the failing boundary (same key + same ID) and the valid boundary (same key, different ID) edge cases are now covered against the real view pager.

Does this PR introduce a breaking change?

• Yes
• No

Other information

All unit tests pass (python -m pytest test/unit: 686 passed, 616 subtests) and pylint is 10.00/10.

Link to Devin session: https://app.devin.ai/sessions/e56da993489d48cfa1f13639d1d84fd9
Requested by: @eml2026