improvement: auto-add OpenLoopPositionEstimator in simulation mode

[jimsynz]

Summary

• Automatically creates OpenLoopPositionEstimator sensors for actuators in simulation mode
• Fixes OpenLoopPositionEstimator to handle PubSub message format

Problem

When using bb_liveview with a robot that has actuators defined (like bb_example_wx200), moving joint sliders in simulation mode didn't update the 3D visualisation. This was because:

1. Simulated actuators (BB.Sim.Actuator) publish BeginMotion messages, not JointState
2. JointState messages are needed for the visualisation to update
3. Users had to manually add OpenLoopPositionEstimator sensors to convert BeginMotion → JointState

Solution

When a robot starts with simulation: :kinematic, the JointSupervisor now automatically creates OpenLoopPositionEstimator sensors for each actuator that doesn't already have one. The auto-generated sensors are named :{actuator_name}_position_estimator.

This ensures simulation mode works out of the box without requiring manual sensor configuration.

Changes

lib/bb/joint_supervisor.ex

• Add build_auto_position_estimators/4 to create sensors for actuators without existing position feedback
• Add has_position_sensor_for_actuator?/2 to check if an actuator already has position feedback

lib/bb/sensor/open_loop_position_estimator.ex

• Add handle_info/2 clause for {:bb, path, message} tuple format from PubSub

test/bb/sim/simulation_test.exs

• Add tests for automatic position estimator creation
• Test that auto estimator is not added when manual one exists
• Test that auto estimator publishes JointState messages
• Test that auto estimator is not added in hardware mode

Test plan

• All existing tests pass
• New tests for auto position estimator pass
• mix check --no-retry passes (except pre-existing flaky test)
• Manual test with bb_example_wx200 in simulation mode