fix: merge logUsage + saveUsageStats to prevent duplicate usage stats for streaming requests

- Enhanced saveUsageStats to include cache tokens (cache_read, cache_creation), reasoning tokens, and estimated flag
- Replaced logUsage calls in stream.js with saveUsageStats (2 locations)
- Removed duplicate saveUsageStats call from streamingHandler.js onStreamComplete
- Removed logUsage function and unused imports from usageTracking.js
- Each streaming request now writes exactly 1 usage record instead of 2

open-sse/handlers/chatCore/streamingHandler.js

@@ -5,7 +5,7 @@ import { pipeWithDisconnect } from "../../utils/streamHandler.js";
 import { PROVIDERS } from "../../config/providers.js";
 import { STREAM_STALL_TIMEOUT_MS } from "../../config/runtimeConfig.js";
 import { buildAbortedResponsesTerminalBytes } from "../../utils/responsesStreamHelpers.js";
-import { buildRequestDetail, extractRequestConfig, saveUsageStats } from "./requestDetail.js";
+import { buildRequestDetail, extractRequestConfig } from "./requestDetail.js";
 import { saveRequestDetail } from "@/lib/usageDb.js";
 
 const SSE_HEADERS = {
@@ -99,8 +99,6 @@ export function buildOnStreamComplete({ provider, model, connectionId, apiKey, r
     }, { id: streamDetailId })).catch(err => {
       console.error("[RequestDetail] Failed to update streaming content:", err.message);
     });
-
-    saveUsageStats({ provider, model, tokens: usage, connectionId, apiKey, endpoint: clientRawRequest?.endpoint, label: "STREAM USAGE" });
   };
 
   return { onStreamComplete, streamDetailId };