move the empty list into init

aider/coders/base_coder.py

@@ -44,7 +44,6 @@ class Coder:
     repo_map = None
     functions = None
     total_cost = 0.0
-    chat_completion_call_hashes = []
 
     @classmethod
     def create(
@@ -104,6 +103,8 @@ class Coder:
         if not fnames:
             fnames = []
 
+        self.chat_completion_call_hashes = []
+
         self.verbose = verbose
         self.abs_fnames = set()
         self.cur_messages = []