test(plugins): add parser unit tests for scapy_recon plugin (#1431)

[Khanvilkarshravani27]

Description

Adds a dedicated parser unit test suite for the scapy_recon plugin to protect parser behaviour from regressions.

The new test file (testing/backend/test_scapy_recon_parser.py) includes 38 tests that cover:

• Metadata contract: Validates metadata.json structure, required fields, engine binary, and output parser type.
• Normal ARP output: Verifies correct IP + MAC extraction, finding keys, category, severity, description, and remediation.
• ICMP output: Verifies hosts with no MAC address default to "Unknown".
• Edge cases: Ensures the parser handles single hosts, empty inputs, whitespace-only, malformed strings, mixed valid/noise lines, and large subnet outputs (50 hosts) without crashing.

Related Issues

Closes #1431

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
• Testing (Adds missing parser test coverage for an existing plugin)

How Has This Been Tested?

Ran the test suite locally using pytest to ensure all new and existing tests pass:

python -m pytest testing/backend/test_scapy_recon_parser.py -v --noconftest

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.