Recover low state source timestamps

[schmidma]

Summary

• recover /low_state source times by matching low-state motor values to /joint_states
• publish low-state-derived ROS-Z topics with the matched vendor timestamp
• allow joint_states through the K1 Zenoh DDS bridge config

Motivation

/low_state has no embedded timestamp, so the bridge previously tagged it with receive/republish time. Matching to /joint_states.header.stamp removes receive-path jitter for IMU and motor-state consumers.

Implementation

• add Publisher::publish_with_source_time
• add ros2::sensor_msgs::joint_state::JointState
• buffer recent low-state and joint-state samples in low_state_bridge
• match exact f32 bit keys for position, velocity, and effort/torque
• drop stale or non-monotonic matches instead of publishing guessed timestamps

Verification

• cargo nextest run -p ros-z -p low_state_bridge
• cargo build -p ros2 -p low_state_bridge -p hulk_ros_z
• cargo fmt --check

[alexschmander]

LGTM