Remove node id dep from mixnet and fix columns access

da/common.py

@@ -1,9 +1,12 @@
 from dataclasses import dataclass
-from typing import List
+from typing import List, Generator
 
 from eth2spec.eip7594.mainnet import Bytes32
 
 
+class NodeId(Bytes32):
+    pass
+
 class Chunk(Bytes32):
     pass
 
@@ -17,7 +20,11 @@ class Row(List[Chunk]):
 
 
 class ChunksMatrix(List[Row]):
-    pass
+    def columns(self) -> Generator[List[Chunk], None, None]:
+        # TODO: yield columns
+        yield None
+
+
 
 
 @dataclass

da/dispersal.py

@@ -1,9 +1,8 @@
 from typing import List, Optional, Generator
 
-from da.common import Certificate
+from da.common import Certificate, NodeId
 from da.encoder import EncodedData
 from da.verifier import DABlob, Attestation
-from mixnet.node import NodeId
 
 
 class Dispersal:
@@ -14,7 +13,7 @@ class Dispersal:
     def _prepare_data(self, encoded_data: EncodedData) -> Generator[DABlob, None, None]:
         assert len(encoded_data.row_commitments) == len(self.nodes)
         assert len(encoded_data.row_proofs) == len(self.nodes)
-        columns = encoded_data.columns
+        columns = encoded_data.extended_matrix.columns()
         column_commitments = encoded_data.column_commitments
         row_commitments = encoded_data.row_commitments
         rows_proofs = encoded_data.row_proofs