test: add parser regression tests for cloud_scanner

[Tuba1809]

Description

Adds focused regression tests for the cloud_scanner parser to improve coverage of malformed, blank, whitespace-only, and noisy input while keeping the production parser behavior unchanged.

Changes Made

• Added regression test for whitespace-only input
• Added regression test for malformed parser output
• Added test to verify the parser handles unrelated noisy lines safely
• Added test to ensure valid findings are preserved when mixed with noisy lines
• Added test to verify a stable result shape for empty parser output
• Confirmed the parser does not raise exceptions for blank, whitespace-only, or malformed input
• No production code was modified; only backend test coverage was expanded

Related Issues

Fixes #2091

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

The focused backend parser test was executed locally.

python -m pytest testing/backend/test_cloud_scanner_plugin.py -v

Result: All tests passed successfully.

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code where appropriate.
• I have made corresponding changes to the documentation. (Not applicable for test-only changes.)
• My changes generate no new warnings.

[utksh1]

Reviewed the focused test change and its current checks are green. The PR still needs a current branch update before merge because it is behind main; I will not bypass the branch policy.