ParallelAgent stops sibling branches on nested sub-agent escalation

## Description

In adk-java, `ParallelAgent` stops all parallel branches when **any** event has `escalate=true`, including escalation from nested sub-agents (for example, an agent running inside a `LoopAgent` sub-branch).

In adk-python, parallel early-exit only happens when the escalating event comes from a **direct** sub-agent:

```python
# parallel_agent.py — _asks_this_agent_to_exit
return bool(event.actions.escalate) and event.author in sub_agent_names