Upkie 3.4.0

This release switches the right leg from bus 2 to bus 3, along with a batch of fixes to the Bullet spine and Gymnasium environments. It also moves agents (aside from the demo PID balancer) to their own repositories:

• MPC balancer: balance in place using model predictive control.
• Pink balancer: an extended PID balancer than can crouch and lift its legs.
• PPO balancer: balance in place with a policy trained by reinforcement learning.

Added

• Add --build argument to the simulation script
• CICD: Run ShellCheck on scripts
• Clear shared-memory when starting the Bullet spine
• Script to dump all servo motor-driver configurations

Changed

• dependencies: Update Upkie description to 1.5.0
• dependencies: Update Vulp to 2.2.1
• Don't build simulation spine if execution fails
• Move agents' requirements.txt files to optional project dependencies
• palinode: Rename run_pid_balancer.sh to try_pid_balancer.sh 😊
• Rename top-level run script to run_pid_balancer.sh

Fixed

• Fix Gymnasium API in the readme example (thanks to @araffin)
• Handle closing of GUI window in simulation script
• Make sure all UpkieServos box observations are proper arrays

Removed

• Move MPC balancer to its own repository
• Move PPO balancer to its own repository