feat: add extended types serializer (#74)

Implement ExtendedTypesSerDes

- Plain JSON for primitives (str, int, float, bool, None)
- Plain JSON for simple lists containing only primitives
- Extended format for complex types (datetime, Decimal, UUID, etc.)
- Support datetime/date with ISO format encoding
- Handle Decimal with string representation

Signed-off-by: Rares Polenciuc <rarepolz@amazon.com>

Author: rarepolz

src/aws_durable_execution_sdk_python/exceptions.py

@@ -168,3 +168,7 @@ def __str__(self) -> str:
             A string in the format "type: message"
         """
         return f"{self.type}: {self.message}"
+
+
+class SerDesError(DurableExecutionsError):
+    """Raised when serialization fails."""