Fix retry offset calculation - use totalEncodedBytesProcessed to request new bytes

The root cause was using getRetryOffset() (which subtracts pending bytes) to determine what to request from the server. This caused requesting bytes we already have in the pending buffer, creating duplicates.

The correct logic:
- totalEncodedBytesProcessed tracks ALL bytes we've received from the server (including those in pending)
- pending buffer holds bytes waiting for more data to complete a structure
- When retrying, we need to request NEW bytes starting from totalEncodedBytesProcessed
- The pending buffer will be combined with new bytes in the policy's decodeStream method

Example:
1. Request bytes=0-, get byte 0, totalEncodedBytesProcessed=1, pending=[0]
2. IOException, retry requesting bytes=1- (starting from totalEncodedBytesProcessed=1)
3. Get byte 1, combine with pending [0] + [1] = [0,1], totalEncodedBytesProcessed=2
4. Still insufficient, pending=[0,1], continue...

This ensures:
- No duplicate bytes from server
- Pending buffer accumulates across retries
- Decoder receives continuous byte stream
- Smart retry resumes from correct offset

Addresses comment #2499104452.

Co-authored-by: gunjansingh-msft <[email protected]>

Author: Copilot

sdk/storage/azure-storage-blob/src/main/java/com/azure/storage/blob/specialized/BlobAsyncClientBase.java

@@ -1407,9 +1407,10 @@ Mono<BlobDownloadAsyncResponse> downloadStreamWithResponse(BlobRange range, Down
                             if (decoderStateObj instanceof StorageContentValidationDecoderPolicy.DecoderState) {
                                 DecoderState decoderState = (DecoderState) decoderStateObj;
 
-                                // Use the retry offset (encoded bytes processed minus pending buffer)
-                                // The pending buffer contains bytes that have been counted but not yet successfully processed
-                                long encodedOffset = decoderState.getRetryOffset();
+                                // Use totalEncodedBytesProcessed to request NEW bytes from the server
+                                // The pending buffer already contains bytes we've received, so we request
+                                // starting from the next byte after what we've already received
+                                long encodedOffset = decoderState.getTotalEncodedBytesProcessed();
                                 long remainingCount = finalCount - encodedOffset;
                                 retryRange = new BlobRange(initialOffset + encodedOffset, remainingCount);