Use bytearray instead of itertools.repeat

from the docs:
> Creating a zero-filled instance with a given length: bytearray(10)

this has the highest likelihood of using a low-level implementation
(hopefully, calloc) to allocate and zero the new array.

- fix lint - remove dead import

Author: charles-cooper

eth/vm/memory.py

@@ -1,4 +1,3 @@
-import itertools
 import logging
 
 from eth._utils.numeric import (
@@ -32,7 +31,7 @@ def extend(self, start_position: int, size: int) -> None:
 
         size_to_extend = new_size - len(self)
         try:
-            self._bytes.extend(itertools.repeat(0, size_to_extend))
+            self._bytes.extend(bytearray(size_to_extend))
         except BufferError:
             # we can't extend the buffer (which might involve relocating it) if a
             # memoryview (which stores a pointer into the buffer) has been created by