Serialize ValidationMessage to JSON

[bact]

To fix #330

The serialized validation messages will be something like:

  "validationMessages": [
    {
      "message": "The root element must be of type Bom or software_Sbom. Found: <class 'spdx_python_model.bindings.v3_0_1.software_Package'>",
      "spdxId": "https://swinslow.net/spdx-examples/example1/hello-v3-specv3/SPDXRef-gnrtd4",
      "parentId": "https://swinslow.net/spdx-examples/example1/hello-v3-specv3/document0",
      "elementType": "None"
    }
  ],

[Copilot]

Pull request overview

This PR adds JSON serialization support for validation messages to fix issue #330. The main change introduces a new get_validation_messages_json function that converts ValidationMessage objects into JSON-serializable dictionaries, including optional context details (spdx_id, parent_id, element_type) when verbose mode is enabled. The PR also refactors attribute access in base_checker.py to use defensive getattr calls with defaults.

Key changes:

• Added get_validation_messages_json function to serialize validation messages with optional context details
• Modified output_json method to use the new serialization function instead of simple string conversion
• Applied defensive programming pattern with getattr throughout the output methods in base_checker.py

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
ntia_conformance_checker/report.py	Added get_validation_messages_json function to serialize validation messages to JSON format with optional context details
ntia_conformance_checker/base_checker.py	Updated output methods to use the new JSON serialization function and applied defensive attribute access pattern
a.json	Example output file showing the new JSON structure (should be removed from PR)

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[jspeed-meyers]

LGTM! Thank you.