Spin TransformListener internal node callback groups

[ktyang512]

Summary

• keep the dedicated /tf and /tf_static callback group registered with the
  listener's private executor
• also register the listener-owned internal node so its automatically added
  default callback group makes progress
• cover both dynamic and static-only internal listeners while leaving
  caller-owned node handling unchanged

Fixes #968.

Root cause

The simplified TransformListener(buffer) constructor creates a private node.
With spin_thread=true, it creates a non-auto-added callback group for the TF
subscriptions and registers only that group with its private executor. On
Jazzy, the internal node also has a TimeSource parameter-event subscription
in its default callback group, but that group is never spun.

The fix retains the explicit TF callback-group registration and additionally
adds only optional_default_node_. Using add_node() alone would not register
the deliberately non-auto-added TF group.

Testing

• reproduced the failure before the production change: the nine existing
  listener tests passed and both new dynamic/static cases failed at the
  default-group assertion
• clean-built pinned Jazzy source for tf2, tf2_msgs, and tf2_ros
• complete tf2_ros CTest: 14/14 passed
• targeted transform-listener CTest repeated 10 times: 10/10 passed
• cppcheck, cpplint, lint_cmake, and uncrustify passed
• git diff --check passed

The regression publishes a targeted use_sim_time=true parameter event and
checks that the internal node creates its /clock subscription. It also sends
a dynamic or static transform and verifies that the buffer receives it, which
guards the existing manually registered TF callback group.

Scope

The observed TimeSource failure is Jazzy-specific. Current Rolling no longer
creates this parameter-event subscription. No public API, QoS setting, thread
count, caller-owned node path, or spin_thread=false behavior is changed.

Generative tool disclosure

Generated-by: OpenAI Codex (GPT-5)

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