fix: resolve golangci-lint errcheck warnings

- Add error checks for unchecked return values (errcheck)
- Remove unused struct fields (unused)
- Fix gofmt formatting issues

natsutil/natsutil_test.go

@@ -200,7 +200,7 @@ func BenchmarkEncodeMap(b *testing.B) {
 		"top_k":      10,
 	}
 	for b.Loop() {
-		msgpack.Marshal(data)
+		_, _ = msgpack.Marshal(data)
 	}
 }
 
@@ -212,7 +212,7 @@ func BenchmarkEncodeStruct(b *testing.B) {
 		Active:    true,
 	}
 	for b.Loop() {
-		msgpack.Marshal(data)
+		_, _ = msgpack.Marshal(data)
 	}
 }
 
@@ -226,7 +226,7 @@ func BenchmarkDecodeMap(b *testing.B) {
 	})
 	for b.Loop() {
 		var m map[string]any
-		msgpack.Unmarshal(raw, &m)
+		_ = msgpack.Unmarshal(raw, &m)
 	}
 }
 
@@ -239,7 +239,7 @@ func BenchmarkDecodeStruct(b *testing.B) {
 	})
 	for b.Loop() {
 		var m testMessage
-		msgpack.Unmarshal(raw, &m)
+		_ = msgpack.Unmarshal(raw, &m)
 	}
 }
 
@@ -251,6 +251,6 @@ func BenchmarkDecodeAudio32KB(b *testing.B) {
 	})
 	for b.Loop() {
 		var m audioMessage
-		msgpack.Unmarshal(raw, &m)
+		_ = msgpack.Unmarshal(raw, &m)
 	}
 }