Issue 1: 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.

Issue 2: Standardize Hook Callback Signatures with **kwargs

Problem

Lifecycle hooks in AgentHooks and RunnerHooks were inconsistent:
on_handoff used **kwargs.
Other hooks like on_agent_start, on_tool_end, etc., used positional arguments.
This inconsistency led to:
Poor developer experience (requiring memorization of argument order).
Risk of bugs and lower maintainability.

Changes

Refactored all hook signatures to accept **kwargs.
Affected hooks include:
on_agent_start
on_agent_end
on_tool_start
on_tool_end
Internal invocation already uses named arguments, so no functional change occurred.

Impact

Improves consistency across the SDK.
Simplifies custom hook implementations.
Enables forward-compatible API evolution.