Document and provide examples for vendor/proprietary parser extensions

[RonanB96]

Make it easy for consumers to add vendor-specific parsers and show examples.

Tasks:

• Add examples/vendor_parsers/register_parsers.py demonstrating runtime registration of custom parsers for non-SIG UUIDs.
• Document extension pattern in docs/usage.md with step-by-step instructions and sample payloads.
• Add tests that run translator against sample payloads with registered vendor parsers.

Acceptance criteria:

• Example script registers parsers and parser output matches expected values.