chore: Add modelName, sessionId, requestId usage (#5670)

https://linear.app/thirdweb/issue/DASH-574/add-nebula-usage-tracker-events

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## PR-Codex overview
This PR introduces additional properties to the `usageEventSchema` in the `service-utils` package, enhancing the tracking of usage events by including identifiers for the model, session, and request.

### Detailed summary
- Added `modelName`, `sessionId`, and `requestId` as optional string fields to the `usageEventSchema` in `packages/service-utils/src/core/usage.ts`.

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.changeset/gold-gorillas-clap.md

@@ -0,0 +1,5 @@
+---
+"@thirdweb-dev/service-utils": patch
+---
+
+Add modelName, sessionId, requestId to usage

packages/service-utils/src/core/usage.ts

@@ -78,5 +78,8 @@ export const usageEventSchema = z.object({
   providerIp: z.string().optional(),
   promptTokens: z.number().int().nonnegative().optional(),
   completionTokens: z.number().int().nonnegative().optional(),
+  modelName: z.string().optional(),
+  sessionId: z.string().optional(),
+  requestId: z.string().optional(),
 });
 export type UsageEvent = z.infer<typeof usageEventSchema>;