test: add coverage for zap scanner plugin

[deepsikha-dash]

Description

• Added direct parser and contract coverage for the zap_scanner plugin.
• Added a deterministic fixture for parser testing.
• Verified plugin metadata loading through the validation path.
• Verified command rendering for representative target inputs.
• Verified parser output normalization into stable SecuScan findings/results.

Related Issues

Closes #521

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?

Executed:

pytest testing/backend/unit/test_zap_scanner_plugin.py -v

Result:

5 passed

The test suite verifies:

• Plugin metadata loading
• Command rendering
• Parser fixture output
• Empty output handling
• Executor normalization behavior

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, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.

[utksh1]

Focused parser/contract coverage for zap_scanner. The fixture expectations match the current metadata, command template, parser behavior, and executor normalization contract.