Speed up plain text frame helper (#692)

aioesphomeapi/_frame_helper/plain_text.pxd

@@ -21,9 +21,9 @@ cdef class APIPlaintextFrameHelper(APIFrameHelper):
         add_length=bytes,
         end_of_frame_pos=cython.uint,
         length_int=cython.uint,
-        preamble=cython.uint,
-        length_high=cython.uint,
-        maybe_msg_type=cython.uint
+        preamble=char,
+        length_high=char,
+        maybe_msg_type=char
     )
     cpdef data_received(self, object data)
 

aioesphomeapi/_frame_helper/plain_text.py

@@ -16,7 +16,7 @@ def _varuint_to_bytes(value: _int) -> bytes:
     if value <= 0x7F:
         return bytes((value,))
 
-    result = []
+    result = bytearray()
     while value:
         temp = value & 0x7F
         value >>= 7