test : added unit tests for build_asset_summary and related helpers

[tmdeveloper007]

Closes #1247.

Summary of What Has Been Done:
Added unit tests for build_asset_summary and related helpers in backend/secuscan/finding_intelligence.py: _normalize_url_path, _typed_evidence, and build_asset_summary. Tests cover URL normalization, evidence item normalization with confidence clamping, and asset-level finding aggregation.

Changes Made:

• Created testing/backend/unit/test_finding_intelligence_asset_summary.py with 21 test cases
• _normalize_url_path: 8 tests (full URLs, relative paths, root paths, trailing slashes, empty)
• _typed_evidence: 7 tests (dict/non-dict items, confidence clamping, override behavior)
• build_asset_summary: 6 tests (empty inputs, findings only, services only, severity ranking, sorting)

Impact it Made:

• Guards asset-level finding aggregation logic against regressions
• Tests URL normalization edge cases (relative vs absolute paths)
• Increases overall test coverage of the finding_intelligence module

Note: This task is being handled by tmdeveloper007 -- please assign to that account when picking it up.