Increase upsert queue size, fix stream disposal timing

Refactored MemoryStream handling during bulk upserts to ensure
streams are disposed only after the Cosmos DB SDK completes
reading, preventing premature disposal and potential errors.

Author: Andrii Bondarchuk

src/FitSyncHub.Functions/Functions/EverestingHOFScraperHttpTriggerFunction.cs

@@ -214,20 +214,37 @@ private async Task<List<UpsertResult>> UpsertActivities(
         foreach (var activity in activities.EnumerateArray())
         {
             // Convert JsonElement → stream
-            await using var stream = new MemoryStream();
+            var stream = new MemoryStream(); //do not dispose, will be disposed after SDK read
             await using (var writer = new Utf8JsonWriter(stream))
             {
                 activity.WriteTo(writer);
             }
 
             stream.Position = 0;
 
-            // Upsert in bulk
-            tasks.Add(_everestingHOFContainer.UpsertItemStreamAsync(
-                stream,
-                new PartitionKey(activity.GetProperty("id").GetString()),
-                cancellationToken: cancellationToken)
-            );
+            var id = activity.GetProperty("id").GetString()!;
+
+            // Upsert in bulk — SDK may read/clone the stream asynchronously, so do not dispose it here
+            tasks.Add(TaskToUpsertItemAndCloseStream(stream, id, cancellationToken));
+
+            async Task<ResponseMessage> TaskToUpsertItemAndCloseStream(MemoryStream stream, string id, CancellationToken cancellationToken)
+            {
+                try
+                {
+                    return await _everestingHOFContainer.UpsertItemStreamAsync(
+                        stream,
+                        new PartitionKey(id),
+                        cancellationToken: cancellationToken);
+                }
+                catch (Exception)
+                {
+                    throw;
+                }
+                finally
+                {
+                    await stream.DisposeAsync();
+                }
+            }
         }
 
         var result = new List<UpsertResult>();