Add projections and tests!

[zeerekahmad]

Description

Integrates the shared polymath_kinematics::ArticulatedModel into the articulated steering controller,
replacing the controller's hand-rolled kinematic formulas with the library used across the fleet. The
two previously-separate command paths (front_two_wd and four_wd, each with its own
get_velocity_command* / calculate_wheel_speed* pair) collapse into a single
get_velocity_command,
which derives the steering target from bodyVelocityToVehicleState and the per-wheel speeds from
articulationToAxleVelocities, with drive_mode deciding whether the rear wheels are driven or zeroed.

Beyond the kinematics swap, the controller gains proper signal conditioning and real odometry. Linear
velocity now passes through a first-order lag (time constant τ) that models drivetrain inertia instead
of the old ad-hoc filtering, and the articulation angle is rate-limited toward its target to model
hydraulic cylinder speed. The update() loop integrates pose (x, y, θ) from the measured wheel speeds
and articulation angle and publishes real odometry (pose + twist) via a tf2 quaternion, and parameters
are re-read every tick so they can be retuned at runtime.

• src/articulated_steering_controller.cpp:
  constructs the ArticulatedModel on configure and validates the wheel-joint count against
  drive_mode; unifies the command path into get_velocity_command (general/straight-line via
  bodyVelocityToVehicleState, explicit pure-rotation and stop cases); first-order velocity lag,
  rate-limited steering, wheel speeds from articulationToAxleVelocities; odometry integrated in
  update() and published with real pose/twist; dynamic parameter reload each tick.
• include/…/articulated_steering_controller.hpp:
  adds a std::unique_ptr<polymath::kinematics::ArticulatedModel> member, odometry state
  (odom_x_/odom_y_/odom_theta_, cached measured twist, last_odom_time_), and the
  velocity_time_constant_ / steering_rate_ tuning members; removes the now-dead
  get_velocity_command_front_2wd, calculate_wheel_speed, and calculate_wheel_speed_front_2wd
  declarations — unified into the single get_velocity_command.
• src/articulated_steering_controller_parameters.yaml:
  replaces publish_rate with velocity_time_constant (first-order lag τ, default 0.5 s) and
  steering_rate (max articulation rate, default 1.0 rad/s), both validated > 0.
• CMakeLists.txt
  and package.xml:
  add polymath_kinematics, tf2, and tf2_geometry_msgs as link/build dependencies.
• repos-humble.yaml / repos-jazzy.yaml: add the
  polymath_kinematics git repository so vcs import pulls it into the workspace.

Migration Guide

Two migration steps for anyone deploying or building against this controller:

1. New dependency polymath_kinematics. It is now a build/runtime dependency of
   articulated_steering_controller. Re-run vcs import with the updated repos-humble.yaml /
   repos-jazzy.yaml to fetch it, then rebuild. Downstream packages that depend on the controller
   rebuild transitively.
2. publish_rate parameter removed. Any articulated_steering_controller config that sets
   publish_rate must drop it. It is superseded by velocity_time_constant (τ for the linear-velocity
   lag, default 0.5 s) and steering_rate (max articulation rate, default 1.0 rad/s). Defaults preserve
   sensible behavior, so setting them is optional.

Related issues

closes #6

Completeness checklist

• Is there test coverage? If it was a bugfix, is there a regression test?
• Is user-facing API/behavior documented?
• Is core documentation updated?
• Are all checks green?
• Assign reviewers to the PR and post in #code_reviews