fix: Channel's recursive_close issue

[IthacaDream]

Fixes: #25

Summary

• Fix recursive_close in Channel.run_in_ctx to always traverse all children and then close the current channel if running.
• This ensures a consistent, bottom-up shutdown across the entire channel tree.

What changed

• Removed the early return when a node has no children.
• Removed the if not child.is_running() guard; always recurse into every child.

Verification

• run pytest tests/channels/test_thread_channel.py::test_channel_run_in_ctx_closes_child_channels

[IthacaDream]

This if-condition is inverted