fix: Not all code vectors are user assigned

lib/medical_transcription/transcriptions/transcription_chunk_code_vector.ex

@@ -1,4 +1,8 @@
 defmodule Medicode.Transcriptions.TranscriptionChunkCodeVector do
+  @moduledoc """
+  Represents a code vector assigned to a transcription chunk.
+  """
+
   use Ecto.Schema
   import Ecto.Changeset
 
@@ -28,8 +32,7 @@ defmodule Medicode.Transcriptions.TranscriptionChunkCodeVector do
     |> validate_required([
       :transcription_chunk_id,
       :code_vector_id,
-      :cosine_similarity,
-      :assigned_by_user_id
+      :cosine_similarity
     ])
   end
 end