Refactor concurrency handling to utilize SweepstoreWorkerTicketSnapshot for improved state management and add snapshot method in header.dart

dart/lib/header.dart

@@ -359,4 +359,58 @@ class SweepstoreWorkerTicket {
       return false;
     }
   }
+
+  SweepstoreWorkerTicketSnapshot snapshot() {
+
+    _concurrencyHeader._header._file.lockSync(FileLock.blockingShared, _baseOffset, _baseOffset + ticketSize);
+
+    _concurrencyHeader._header._file.setPositionSync(_baseOffset);
+    List<int> existingBuffer = _concurrencyHeader._header._file.readSync(ticketSize);
+    RandomAccessMemory buffer = RandomAccessMemory(existingBuffer);
+    _concurrencyHeader._header._file.unlockSync(_baseOffset, _baseOffset + ticketSize);
+
+    buffer.setPositionSync(0);
+    int identifier = buffer.readIntSync(4);
+    int workerHeartbeat = buffer.readIntSync(4);
+    SweepstoreTicketState ticketState = SweepstoreTicketState.values[buffer.readIntSync(1)];
+    SweepstoreTicketOperation ticketOperation = SweepstoreTicketOperation.values[buffer.readIntSync(1)];
+    int keyHash = buffer.readIntSync(8);
+    SweepstorePointer writePointer = SweepstorePointer(buffer.readIntSync(8));
+    int writeSize = buffer.readIntSync(4);
+    return SweepstoreWorkerTicketSnapshot._(
+      ticketIndex: ticketIndex,
+      identifier: identifier,
+      workerHeartbeat: workerHeartbeat,
+      ticketState: ticketState,
+      ticketOperation: ticketOperation,
+      keyHash: keyHash,
+      writePointer: writePointer,
+      writeSize: writeSize,
+    );
+  }
+
+}
+
+class SweepstoreWorkerTicketSnapshot {
+
+  final int ticketIndex;
+  final int identifier;
+  final int workerHeartbeat;
+  final SweepstoreTicketState ticketState;
+  final SweepstoreTicketOperation ticketOperation;
+  final int keyHash;
+  final SweepstorePointer writePointer;
+  final int writeSize;
+
+  SweepstoreWorkerTicketSnapshot._({
+    required this.ticketIndex,
+    required this.identifier,
+    required this.workerHeartbeat,
+    required this.ticketState,
+    required this.ticketOperation,
+    required this.keyHash,
+    required this.writePointer,
+    required this.writeSize,
+  });
+
 }