separate typing imports try/except from sturct import try/except

The changes to add type hints accidentally made the module
non-importable on circuitpython boards.

I'm not sure whether we need to keep the `ustruct` compatibility
(it would only apply to micropython) but go ahead and do so.

Closes: #36

Author: jepler

adafruit_fingerprint.py

@@ -30,6 +30,10 @@
 try:
     from typing import Tuple, List, Union
     from busio import UART
+except ImportError:
+    pass
+
+try:
     import struct
 except ImportError:
     import ustruct as struct