fix: exclude initialization time from upload time calculation (#4052)

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This PR changes the upload time calculation to only include actual
uploading time, excluding initialization time.

**New behavior:**
When resources and network are limited:
- File A and B initialize simultaneously. File B's initialization takes
longer.
- When File B starts uploading, its timer starts at 0s and tracks only
its upload duration.


https://github.com/user-attachments/assets/6dc3af4f-d7e6-408e-9ce9-011e104ef294


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Fixes #4051

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Passed automated tests, manually tested with large uploads

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No

Author: xuang7

frontend/src/app/dashboard/service/user/dataset/dataset.service.ts

@@ -157,15 +157,20 @@ export class DatasetService {
       const partProgress = new Map<number, number>();
 
       // Progress tracking state
-      const startTime = Date.now();
+      let startTime: number | null = null;
       const speedSamples: number[] = [];
       let lastETA = 0;
       let lastUpdateTime = 0;
 
       // Calculate stats with smoothing
+      const getTotalTime = () => (startTime ? (Date.now() - startTime) / 1000 : 0);
       const calculateStats = (totalUploaded: number) => {
+        if (startTime === null) {
+          startTime = Date.now();
+        }
+
         const now = Date.now();
-        const elapsed = (now - startTime) / 1000;
+        const elapsed = getTotalTime();
 
         // Throttle updates to every 1s
         const shouldUpdate = now - lastUpdateTime >= 1000;
@@ -324,7 +329,6 @@ export class DatasetService {
                 )
               ),
               tap(() => {
-                const finalTotalTime = (Date.now() - startTime) / 1000;
                 observer.next({
                   filePath,
                   percentage: 100,
@@ -333,13 +337,12 @@ export class DatasetService {
                   physicalAddress: physicalAddress,
                   uploadSpeed: 0,
                   estimatedTimeRemaining: 0,
-                  totalTime: finalTotalTime,
+                  totalTime: getTotalTime(),
                 });
                 observer.complete();
               }),
               catchError((error: unknown) => {
                 // If an error occurred, abort the upload
-                const currentTotalTime = (Date.now() - startTime) / 1000;
                 observer.next({
                   filePath,
                   percentage: Math.round((uploadedParts.length / partCount) * 100),
@@ -348,7 +351,7 @@ export class DatasetService {
                   physicalAddress: physicalAddress,
                   uploadSpeed: 0,
                   estimatedTimeRemaining: 0,
-                  totalTime: currentTotalTime,
+                  totalTime: getTotalTime(),
                 });
 
                 return this.finalizeMultipartUpload(