v6.0.0: Update agent-spine IPC

[stephane-caron]

This release gives one more careful 👀 to spine cycles, with the main two updates:

• Combine action and observation steps in the spine-agent IPC protocol, halving the number of waiting intervals between the two.
• Fix observation consistency between the run and simulate spine functions: thanks to @Tordjx for pointing this out 👍

This iteration also produced some more design documentation in the following discussions:

• Starting CAN cycles after sleep or after action
• Shift in actions sequence between agent and simulator

Added

• Makefile: Conda environment packing and unpacking rules
• Support Python 3.12
• tools: Add ps_thread command

Changed

• Breaking: Spine and spine interface revisions:
  • Observations are now returned upon reset and step
  • Spine: Remove separate observation state and observation request
  • SpineInterface: Setting an action now returns an observation
  • SpineInterface: Starting the spine now returns an observation
  • StateMachine: Rename spine FSM state from "act" to "step"
  • docs: Update spine FSM specification in the documentation
• Breaking: actuation: Move resolution to static configuration
• Breaking: actuation: Move servo layout to static configuration
• Breaking: envs: Rename LowPassFilterAction to AddLagToAction
• CICD: Pin Ubuntu workflows to 22.04
• Default kd gain for wheel servos is now 0.3
• Move Python spine exceptions to upkie.exceptions
• docs: Turn environment page into an index
• tools: Make output directory an argument in dump_servo_configs
• tools: Simplify servo configuration script

Fixed

• BulletInterface: Fix typo in a comment
• CICD: Install Doxygen with specific version from conda-forge
• Spine: Fix observation consistency between run and simulate
• envs: Clamp ground velocity action in UpkieGroundVelocity

Removed

• Bazel: Remove legacy rules for PyPI dependencies
• Move PID balancer to its own repository
• deps: Remove dependency on PyYAML
• examples: Remove Bazel BUILD file
• model: Remove duplicate maximum torque constant

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This discussion was created from the release v6.0.0.