feat: add e2e tests + benchmarks

- e2e_test.go: Argo/Kubeflow full payload validation, concurrent requests
- Pipeline dispatch validation, unknown pipeline error handling
- Benchmarks: Argo 218µs/op, Kubeflow 179µs/op

main.go

@@ -122,7 +122,7 @@ func submitArgo(ctx context.Context, client *http.Client, host, namespace, templ
 		},
 		"spec": map[string]any{
 			"workflowTemplateRef": map[string]string{"name": template},
-			"arguments":          map[string]any{"parameters": argoParams},
+			"arguments":           map[string]any{"parameters": argoParams},
 		},
 	}