test : added unit tests for _fingerprint_score and build_scan_diff in finding_intelligence

[tmdeveloper007]

Closes #1727. Closes #1728.

Summary of What Has Been Done:
Created testing/backend/unit/test_finding_intelligence_fingerprint.py covering two previously untested functions in finding_intelligence.py.

Changes Made:

• New file: testing/backend/unit/test_finding_intelligence_fingerprint.py
  • TestFingerprintScore (12 tests): _fingerprint_score tuple shape, determinism, match_strength variants, validated flag handling, case insensitivity, unknown strength fallback
  • TestBuildScanDiff (12 tests): build_scan_diff new/resolved/changed detection, finding_group_id vs id matching, mixed scenarios, summary totals

Impact it Made:

• Coverage: adds tests for two previously untested functions in a well-tested module
• Reliability: ensures fingerprint score computation and scan diff logic work correctly
• No changes to production code

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

[utksh1]

Closing: this PR is part of the same mass template-generated low-value test batch pattern. The PRs use repetitive boilerplate bodies, copy-pasted structures, and in several cases manufacture tiny helpers or duplicate existing coverage rather than contributing one focused, meaningful improvement. Please submit a smaller, genuinely curated PR if you want to work on one concrete test gap.