Fix Contrast parser collapsing findings with the same rule name

[Jino-T]

[sc-12973]

Summary

• The dupe_key in the Contrast parser was hashed from vuln_id_from_tool (Rule Name), causing all findings of the same rule type (e.g. ldap-injection) to be collapsed into a single finding
• Changed the dupe_key to hash unique_id_from_tool (Vulnerability ID) instead, since each Contrast Vulnerability ID uniquely identifies a distinct finding instance
• The existing merge/aggregation block is retained as a safety net for the edge case of duplicate Vulnerability IDs in a report

Test plan

• test_ldap_multiple_findings — verifies that 3 findings with the same Rule Name but different Vulnerability IDs are returned as 3 distinct findings (regression test for the bug)
• test_duplicate_vuln_id_is_merged — verifies the merge safety net still works when a Vulnerability ID appears twice in a report
• test_example_report and test_example2_report — existing tests updated to reflect correct post-fix finding counts