Cleanup flocking example to use composition

[tychedelia]

Flocking is now built from the generic ops, so the built-in flock goes.

• Removed: p.flock(), particles_flock, particles_kernel_flock, the flock.wgsl kernel, and its FFI constructor.
• flocking_gpu.py is now a recipe with no shader code: find neighbors, sum what each rule steers toward, apply steering with a mask for boids that have no neighbors, then add the force to velocity and limit the speed.

It's slower than the fused kernel: about 3.5 ms vs 1.6 ms at 20k boids, and 8 ms vs 4 ms at 100k. Most of that is the per-dispatch cost of ~30 passes, not GPU work, so batching submits is the next thing to look at. Anyone who needs the speed can still write a small kernel that reads neighbors directly.

[github-actions]

Visual regression: 43 new of 43 cases

case	status	detail
rectangle	🆕 new	no baseline on main
primitives_3d	🆕 new	no baseline on main
particles_noise	🆕 new	no baseline on main
py_primitives_3d	🆕 new	no baseline on main
py_particles_noise	🆕 new	no baseline on main
py_animated_mesh	🆕 new	no baseline on main
py_background_image	🆕 new	no baseline on main
py_blend_modes	🆕 new	no baseline on main
py_box	🆕 new	no baseline on main
py_camera_controllers	🆕 new	no baseline on main
py_curves	🆕 new	no baseline on main
py_custom_material	🆕 new	no baseline on main
py_feedback	🆕 new	no baseline on main
py_flocking	🆕 new	no baseline on main
py_flocking_duck	🆕 new	no baseline on main
py_flocking_gpu	🆕 new	no baseline on main
py_geometry_methods	🆕 new	no baseline on main
py_gltf_load	🆕 new	no baseline on main
py_lights	🆕 new	no baseline on main
py_materials	🆕 new	no baseline on main
py_multi_window	🆕 new	no baseline on main
py_particles_animated	🆕 new	no baseline on main
py_particles_basic	🆕 new	no baseline on main
py_particles_density	🆕 new	no baseline on main
py_particles_emit	🆕 new	no baseline on main
py_particles_emit_gpu	🆕 new	no baseline on main
py_particles_from_mesh	🆕 new	no baseline on main
py_particles_gpu_surface	🆕 new	no baseline on main
py_particles_gpu_surface_lit	🆕 new	no baseline on main
py_particles_lifecycle	🆕 new	no baseline on main
py_particles_lines	🆕 new	no baseline on main
py_particles_lissajous	🆕 new	no baseline on main
py_particles_points	🆕 new	no baseline on main
py_particles_scatter_volume	🆕 new	no baseline on main
py_particles_sphere	🆕 new	no baseline on main
py_particles_stress	🆕 new	no baseline on main
py_particles_surface	🆕 new	no baseline on main
py_primitives_2d	🆕 new	no baseline on main
py_rectangle	🆕 new	no baseline on main
py_shapes	🆕 new	no baseline on main
py_style_stack	🆕 new	no baseline on main
py_text	🆕 new	no baseline on main
py_window_controls	🆕 new	no baseline on main

_{baseline unknown · adapter llvmpipe (LLVM 20.1.2, 256 bits) (Vulkan, Mesa 25.2.8-0ubuntu0.24.04.2 (LLVM 20.1.2))}

Open the visual report · workflow run