Fix ub-test-reports link properties overwriting when mapped to same link field (#2058)

[0xrutabaga]

Summary

Fixes an issue in ub-test-reports where multiple XML properties mapped onto the same link field overwrite each other instead of merging.

Closes #2058.

Problem / Root Cause

In build_need, iterating over link_properties.items() directly assigned need[link_field] = [item.strip() for item in raw.split(",") if item.strip()]. If multiple properties were mapped to the same field, subsequent properties unconditionally replaced earlier ones. Furthermore, if a mapped property was missing from a test case, it evaluated to empty, erasing previously extracted links.

Solution

• Pre-initialize all mapped link_field targets to [].
• For non-empty property values, merge and deduplicate while preserving comma/mapping order using list(dict.fromkeys(existing + items)).
• Leave existing links intact when subsequent mapped properties are absent or empty.
• Added changelog entry in packages/ub-test-reports/docs/changelog.rst.

Tests Added

• Added unit tests in packages/ub-test-reports/tests/test_needs_export.py verifying multi-property merging, deduplication, order preservation, and absent property preservation.
• Added CLI conversion integration test in packages/ub-test-reports/tests/test_cli_convert.py.

Validation

• uv run pytest packages/ub-test-reports/tests/test_needs_export.py: 53 passed.
• uv run pytest packages/ub-test-reports/tests/test_cli_convert.py: 47 passed, 1 skipped.
• uv run pytest packages/ub-test-reports/tests/test_cli_config.py: 36 passed.
• uv run ruff check packages/ub-test-reports: All checks passed.
• uv run ruff format --check packages/ub-test-reports: 24 files clean.
• Limitation: Full repo test test_project_config.py was skipped locally due to Windows symlink privilege limitations.

[chrisjsewell]

Thanks for the quick fix. #2058 is now fixed through #2119, so I'm closing this one in its favour.

#2119 merges the same way (mapping order, each id once, the field still written when empty) and also pins the mapping through the [test_reports.build.needs] link_properties table — the config loader's path, not only the --link-property flags — with a mapping-order control, and documents the rule on the converter's page. Appreciated.