test(plugins): cover duplicate plugin identifier diagnostics #2168

[Rakshak05]

Description

Added loader diagnostics and automated test coverage for handling duplicate plugin identifiers during plugin loading:

• Updated PluginManager in backend/secuscan/plugins.py to maintain a plugin_locations mapping of loaded plugin IDs to directory paths.
• Added duplicate ID detection in load_plugins() that emits an error log identifying both conflicting plugin directory locations when a duplicate ID is encountered.
• Preserved existing safe behavior by skipping the duplicate plugin rather than silently overwriting the already-registered plugin.
• Added unit test test_plugin_loader_duplicate_identifier_diagnostics in testing/backend/unit/test_plugins.py to verify that both conflicting locations are captured in error diagnostics.

Related Issues

Fixes #2168

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 the affected backend unit test suite using pytest:

python -m pytest testing/backend/unit/test_plugins.py testing/backend/unit/test_plugins_validation.py testing/backend/unit/test_plugin_integrity.py

Result: 46 passed in 2.05s (all tests passed cleanly).

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.