fix: Expose extended type via standard dbapi import (#412)

Author: ptiurin

src/firebolt/async_db/__init__.py

@@ -12,6 +12,7 @@
     Binary,
     Date,
     DateFromTicks,
+    ExtendedType,
     Time,
     TimeFromTicks,
     Timestamp,

src/firebolt/db/__init__.py

@@ -10,6 +10,7 @@
     Binary,
     Date,
     DateFromTicks,
+    ExtendedType,
     Time,
     TimeFromTicks,
     Timestamp,