Reference tests: the smaller gaps (collision, math, allocator, container, shape names and flags, joint disable, manifold points, broad phase stress, SIMD width) #146

From the audit of the reference's tests (e77352c): the smaller gaps, each in a file that is otherwise ported.

• test_collision.c: AABBTest's inverted box; the ray cases ending inside, wholly inside, parallel within the slab, a point outside, through a corner and along a face; LargeWorldManifoldTest and LargeWorldAABBTest checked directly. (Ported in the PR for Port the rest of the reference's benchmark suite (design item 16): nine scenes and the SAT runs #141 as tests/test_collision.ae.)
• test_math.c, MathTest: Matrix2 invert and solve (math.invert2, math.solve2 exist untested); the NLerp twist-angle sweep (math.nlerp untested); ArbitraryPerp on the given normal; the full 3x3 m inv(m) components.
• test_allocator.c: TestBlockAllocate, TestBlockClear and TestBlockAlignment. basics.block_allocator_* exists but is not tested.
• test_container.c: TestArrayRemove (reserve capacity, remove-swap draining the array while summing); TestArrayPop (resize, pop to empty); TestStructWithArray.
• test_shape.c: ShapeNameTest (a name on ShapeDef, clearing with null, the over-length truncation) and ShapeFlagsTest (all four flags set from the def, then one flipped while the others hold).
• test_joint.c, TestNonDynamicJointDisable: the set_type path (a dynamic pair welded, then static and kinematic, disabled and enabled, back to dynamic, the joint awake). The direct static-kinematic case is covered.
• test_manifold.c, MaxPointCountTest: get_max_manifold_points equal to the manifold's point capacity.
• test_broad_phase.c: StaticRebuildKeepsMarks (a static body teleported with set_transform, then rebuild_static_tree, then its contact found) and BroadPhaseStressTest (a swarm churning every mutation over height-field tiles: transforms, types, disable and enable, destroy and create, bullets, a collide-connected weld, sleep; the pair set checked against brute force after every step at 1, 4 and 3 workers).
• test_determinism.c, SIMDWidthTest: the RollingMix scene at width 4 and width 8 in one process, bit for bit. The CI's golden trace across -mavx2 builds covers the width as a whole.