[Core] Ensure Node._node_labels initializes regardless of connect_only

[dancingactor]

Description

This PR ensure Node._node_labels initializes regardless of connect_only. The original code only initializesdNode._node_labels when connect_only = true

Related issues

Closes #61604

Additional information

Verification

Testing Script

import ray

ray.init()
print(ray.runtime_context.get_runtime_context().get_node_labels())

Before Fix

Traceback (most recent call last):
  File "/code/labs/jakob/ray/node_labels.py", line 7, in <module>
    print(ray.runtime_context.get_runtime_context().get_node_labels())
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/ray/runtime_context.py", line 598, in get_node_labels
    return worker.current_node_labels
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/ray/_private/worker.py", line 634, in current_node_labels
    return self.node.node_labels
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/ray/_private/node.py", line 685, in node_labels
    return self._node_labels
           ^^^^^^^^^^^^^^^^^
AttributeError: 'Node' object has no attribute '_node_labels'. Did you mean: 'node_labels'?

After Fix

{'ray.io/node-id': 'b32f99e4d621a79a6a001662c1e0fd54b929765b0f69bb12e263c2b7'}

[gemini-code-assist]

Code Review

This pull request addresses an AttributeError by ensuring the _node_labels attribute of the Node class is consistently initialized across all code paths. The security review found no vulnerabilities. The fix involves moving initialization logic out of a conditional block, and a suggestion has been made to enhance robustness against None values.

[edoakes]

@MengjinYan @ryanaoleary PTAL

[ryanaoleary]

Can we add a test for the connect_only = false case?

[dancingactor]

I noticed that _node_labels tests were missing for both connect_only = true and false scenarios, so I added unit tests for each in be4aaa4

[dancingactor]

I also noticed a potential discrepancy in the label's doc, which says that

You can’t set labels using ray.init(). Local Ray clusters don’t support labels."

But we actually can set labels using ray.init(). For example

ray/python/ray/tests/test_node_labels.py

Lines 63 to 65 in aabe458

	def test_ray_init_set_node_labels(shutdown_only):
	labels = {"gpu_type": "A100", "region": "us"}
	ray.init(labels=labels)