Update DateTime class and to_pydatetime function to handle timezo…

…ne information

* Preserve timezone information when converting Python `datetime` objects to C# `System.DateTime` objects
* Handle different date formats and retain timezone information when converting C# `System.DateTime` objects to Python `datetime` objects
* Avoid setting the timezone attribute directly on the datetime class and handle timezone-aware datetime objects correctly using existing methods

stock_indicators/_cstypes/datetime.py

@@ -20,6 +20,8 @@ class DateTime:
         3/26/2021 10:02:22 PM
     """
     def __new__(cls, datetime: PyDateTime) -> CsDateTime:
+        if datetime.tzinfo is not None:
+            datetime = datetime.astimezone(PyTimezone.utc)
         return CsDateTime.Parse(datetime.isoformat(timespec='seconds'))
 
 
@@ -31,7 +33,6 @@ def to_pydatetime(cs_datetime: CsDateTime) -> PyDateTime:
         cs_datetime : `System.DateTime` of C#.
     """
     py_datetime = PyDateTime.fromisoformat(cs_datetime.ToString("o", CsCultureInfo.InvariantCulture))
+    if cs_datetime.Kind == 1:  # 1 indicates UTC
+        py_datetime = py_datetime.replace(tzinfo=PyTimezone.utc)
     return py_datetime
-
-if not hasattr(PyDateTime, 'timezone'):
-    PyDateTime.timezone = PyTimezone