Speed up formatting the cipher nonce (#477)

aioesphomeapi/_frame_helper.py

@@ -4,6 +4,7 @@ import logging
 from abc import abstractmethod
 from enum import Enum
 from functools import partial
+from struct import Struct
 from typing import TYPE_CHECKING, Any, Callable, Optional, cast
 
 import async_timeout
@@ -34,12 +35,19 @@ SOCKET_ERRORS = (
     TimeoutError,
 )
 
+PACK_NONCE = partial(Struct("<LQ").pack, 0)
+
 
 class ChaCha20CipherReuseable(ChaCha20Cipher):  # type: ignore[misc]
+    """ChaCha20 cipher that can be reused."""
+
     @property
     def klass(self):  # type: ignore[no-untyped-def]
         return ChaCha20Poly1305Reusable
 
+    def format_nonce(self, n: int) -> bytes:
+        return PACK_NONCE(n)
+
 
 class ESPHomeNoiseBackend(DefaultNoiseBackend):  # type: ignore[misc]
     def __init__(self, *args: Any, **kwargs: Any) -> None: