fix(sbi): avoid leaking Go types in malformed request errors

[wiwi878]

Related issue

This PR fixes free5gc/free5gc#1128, where malformed SBI request responses expose internal Go model names in ProblemDetails.detail.

Summary

When AMF receives a malformed SBI request body, the error response can expose internal Go model names such as models.AssignEbiData.

This change:

• replaces the exposed parser error with a generic client-facing message;
• keeps the detailed deserialization error in the AMF log;
• returns 400 Bad Request with cause: INVALID_MSG_FORMAT;
• sets the response media type to application/problem+json.

The fix covers the Namf_Communication handlers from #1128 and the same error pattern in Namf_Location, Namf_EventExposure, and AMF callback handlers.

Testing

• go test ./internal/sbi/... passes.
• go test ./... is currently affected by an unrelated timing-sensitive failure in internal/context/TestTimerStartAndStop: the test expected 3 expirations but observed fewer.

Fixes free5gc/free5gc#1128

[d11nn]

Hi @wiwi878,
It seems internal/sbi/api_location.go was missed in this PR. It still has the same pattern in HTTPProvideLocationInfo:

err = openapi. Deserialize(&requestLocInfo, requestBody, "application/json")
if err != nil {
  problemDetail := "[Request Body] " + err. Error() // Still exposes Go struct name
  ... 

Could you also update HTTPProvideLocationInfo in api_location.go with the same fix?

Optional suggestion: Since this error-handling block is now duplicated across ~17 handlers in communication, eventexposure, callback, and location, it might also be worth extracting it into a common helper function in internal/sbi to keep the code clean and avoid missing endpoints in the future

[d11nn]

@Alonza0314 LGTM