fix: Add __str__ and __repr__ methods for better debugging of Server Error and fix the misleading comment in the constructor

Fix class name in __str__ method

Author: aneeshgarg

src/a2a/utils/errors.py

@@ -74,7 +74,7 @@ def __str__(self) -> str:
         if self.error is None:
             return 'None'
         if self.error.message is None:
-            return f'{type(self.error)}'
+            return self.error.__class__.__name__
         return self.error.message
 
     def __repr__(self) -> str: