Apply lots of refactoring to the websocket subpackage (fix every mypy error and warning). Add integers.py and decimal.py to bfxapi.utils package. Update requirements.txt and setup.py with new mypy dependencies.

bfxapi/utils/integers.py

@@ -0,0 +1,35 @@
+from typing import cast, TypeVar
+
+from .. exceptions import IntegerUnderflowError, IntegerOverflowflowError
+
+__all__ = [ "Int16", "Int32", "Int45", "Int64" ]
+
+T = TypeVar("T")
+
+class _Int(int):
+    def __new__(cls: T, integer: int) -> T:
+        assert hasattr(cls, "_BITS"), "_Int must be extended by a class that has a static member _BITS (indicating the number of bits with which to represent the integers)."
+
+        bits = cls._BITS - 1
+
+        min, max = -(2 ** bits), (2 ** bits) - 1
+
+        if integer < min:
+            raise IntegerUnderflowError(f"Underflow. Cannot store <{integer}> in {cls._BITS} bits integer. The min and max bounds are {min} and {max}.")
+
+        if integer > max:
+            raise IntegerOverflowflowError(f"Overflow. Cannot store <{integer}> in {cls._BITS} bits integer. The min and max bounds are {min} and {max}.")
+            
+        return cast(T, super().__new__(int, integer))
+
+class Int16(_Int):
+    _BITS = 16
+
+class Int32(_Int):
+    _BITS = 32
+
+class Int45(_Int):
+    _BITS = 45
+
+class Int64(_Int):
+    _BITS = 64