refactor: streamline usage reporting by consolidating record publishing logic

- Introduced a new method `buildRecord` in `usageReporter` to encapsulate record creation, improving code readability and maintainability.
- Added latency tracking to usage records, ensuring accurate reporting of request latencies.
- Updated tests to validate the inclusion of latency in usage records and ensure proper functionality of the new reporting structure.

sdk/cliproxy/usage/manager.go

@@ -17,6 +17,7 @@ type Record struct {
 	AuthIndex   string
 	Source      string
 	RequestedAt time.Time
+	Latency     time.Duration
 	Failed      bool
 	Detail      Detail
 }