fix(ros2): rclrs 0.8 API + bytes payload mapping

Rewrite tines-ros2/src/node.rs against the rclrs 0.8 API (Context::
default_from_env -> create_basic_executor -> create_node; type-inferred
subscriptions; thiserror-based RclrsError) and switch payloads from
std_msgs String to UInt8MultiArray:

* live topics publish the raw Observation.bytes as data (no UTF-8 lossy);
* inbound callbacks use msg.data verbatim;
* receipts are a 32-byte UInt8MultiArray (peer[..16] ++ id[..16]);
* supply the required MultiArrayLayout { dim: [], data_offset: 0 }.

Bump ros_env 0.1 -> 0.3 so the crate's std_msgs pins rclrs 0.8's rosidl
runtime 0.7 (was 0.6), and update Cargo.lock. Add #[allow(dead_code)] on
ManagedTopic::subscriber (drop-guard for the rcl subscription handle).

Keep the ROS2-free build green; no changes outside tines-ros2/ (and the
Cargo.lock entry).

Cargo.lock

@@ -1498,6 +1498,7 @@ name = "tines-ros2"
 version = "0.3.0"
 dependencies = [
  "rclrs",
+ "ros-env",
  "tines-bt",
  "tines-core",
  "tines-store",