test(api): add comprehensive unit tests for API type structures

[Shivampal157]

This PR adds comprehensive unit tests for API type structures defined in pkg/api/types.go.

Coverage includes:

• JSON marshaling and unmarshaling
• Zero-value and partial field handling
• Table-driven tests for all exported structs

No production code changes are introduced.

[Shivampal157]

Hi @bupd,

This PR adds comprehensive, table-driven unit tests for API type structures in pkg/api/types.go, covering JSON marshal/unmarshal behavior, zero-value handling, and partial fields.
All checks are passing and no production code is modified.

Whenever you get a chance, could you please take a look and let me know if any changes are needed before merge?

Thanks for your time and review!