Allow `RequireApprovalSetting` to accept a callable similar to `ToolFilter`.

[mlabeeb03]

I am creating an agent where I want to set the FunctionTool.needs_approval dynamically based on the description of the tool. e.g. if the tool has an explicit [ALWAYS ASK FOR APPROVAL] string inside its description.
Currently I can not do it because the RequireApprovalSetting does not accept a callable. It only accepts static parameters which does not help my use case because I want this field set dynamically per tool.

There is already a precedent for it in the form of ToolFilter that runs per tool. I want something similar for needs_approval that is executed per tool with the callable that I provide.

Note that there is a function _get_needs_approval_for_tool that does run per tool but the code that would run a callable would never get executed because self._needs_approval_policy is never a callable.

def _get_needs_approval_for_tool(
        self,
        tool: MCPTool,
        agent: AgentBase | None,
    ) -> bool | Callable[[RunContextWrapper[Any], dict[str, Any], str], Awaitable[bool]]:
        """Return a FunctionTool.needs_approval value for a given MCP tool."""

        policy = self._needs_approval_policy

        if callable(policy):
            if agent is None:
                return False

            async def _needs_approval(
                run_context: RunContextWrapper[Any], _args: dict[str, Any], _call_id: str
            ) -> bool:
                result = policy(run_context, agent, tool)
                if inspect.isawaitable(result):
                    result = await result
                return bool(result)

            return _needs_approval

        if isinstance(policy, dict):
            return bool(policy.get(tool.name, False))

        return bool(policy)