update-input-guardrail-name (#1053)

# Ensure Fallback Name Handling in input_guardrail
## Problem
The input_guardrail logic previously allowed the name attribute to be
None if not explicitly provided. This caused issues in downstream
systems such as logging, tracing, or serialization that expect a valid
string name.

## Changes
Introduced fallback logic to assign a default name if name is None.
Guarantees that all function metadata includes a valid string name.
Prevents unpredictable behavior or runtime errors in downstream
processes.

## Impact
Improves system robustness and fault tolerance.
Ensures consistent behavior in tools relying on function names.
No breaking changes introduced.

Author: Quratulain-bilal

src/agents/guardrail.py

@@ -241,7 +241,11 @@ async def my_async_guardrail(...): ...
     def decorator(
         f: _InputGuardrailFuncSync[TContext_co] | _InputGuardrailFuncAsync[TContext_co],
     ) -> InputGuardrail[TContext_co]:
-        return InputGuardrail(guardrail_function=f, name=name)
+        return InputGuardrail(
+            guardrail_function=f,
+            # If not set, guardrail name uses the function’s name by default.
+            name=name if name else f.__name__
+        )
 
     if func is not None:
         # Decorator was used without parentheses