Add find method to sequence group

cacheflow/sequence.py

@@ -76,3 +76,9 @@ class SequenceGroup:
             return len(self.seqs)
         else:
             return len([seq for seq in self.seqs if seq.status == status])
+
+    def find(self, seq_id: int) -> Sequence:
+        for seq in self.seqs:
+            if seq.seq_id == seq_id:
+                return seq
+        raise ValueError(f'Sequence {seq_id} not found.')