SnipeIT asset creation fails with 'model_id field is required' despite providing model_id #18

Issue Description

When creating assets in Snipe-IT using the Go library, the API returns an error stating "The model id field is required" despite model_id being properly included in the request payload.

Reproduction Steps

1. Initialize a Snipe-IT client
2. Create an asset with model_id, status_id and manufacturer_id fields set
3. Call CreateAsset method
4. API returns 200 OK but with error status in the body

Expected Behavior

Asset should be created successfully when model_id is provided

Actual Behavior

API returns JSON with error status: {"status":"error","messages":{"model_id":["The model id field is required."]},"payload":null}

Technical Details

• Using rego library version: [v0.0.0-20250529045826-8981c238fe8d]
• The issue appears to be with JSON serialization - model_id is nested under Method instead of being at the root level:

// Current payload structure (problematic):
{
  "name":"test-asset", 
  "asset_tag":"TAG123",
  "serial":"SN123",
  "Method":{
    "manufacturer_id":1,
    "model_id":2,
    "status_id":2
  }
}

// Expected payload structure:
{
  "name":"test-asset",
  "asset_tag":"TAG123",
  "serial":"SN123",
  "manufacturer_id":1,
  "model_id":2,
  "status_id":2
}

Logs

[2025/07/03 01:19:15 PM] {asset_test} {test_asset_creation.go:168} INFO - Asset payload: {"name":"example-mac-xxxx","asset_tag":"TAG-1751519955","serial":"XXXXXXXXXXXX","Method":{"manufacturer_id":1,"model_id":2,"status_id":2}}
[2025/07/03 01:19:15 PM] {asset_test} {test_asset_creation.go:171} INFO - Attempting to create asset...
[2025/07/03 01:19:15 PM] {snipeit} {snipeit.go:64} DEBUG - url: https://example.snipe-it.domain/api/v1/hardware
[2025/07/03 01:19:16 PM] {snipeit} {snipeit.go:167} INFO - Response Status: 200 OK
[2025/07/03 01:19:16 PM] {snipeit} {snipeit.go:168} DEBUG - Response Body: {"status":"error","messages":{"model_id":["The model id field is required."]},"payload":null}
[2025/07/03 01:19:16 PM] {asset_test} {test_asset_creation.go:178} FATAL - Created asset is nil but no error was returned