API not ported: serialization (tree, height field, compound, ids), worker count at run time, colour counts, SIMD width, max manifold points, shape def names #148

From the audit of the reference's tests (e77352c): API the reference has and its tests exercise, not in the port. Recording, the name cache and the hull database are tracked separately.

Serialization:

• the dynamic tree's save and load (TreeSaveLoadRoundtrip)
• the height field's dump to a file and load (FileRoundtrip)
• the compound's serialize and deserialize (CompoundSerializeRoundtrip, SerializeBadVersion, SerializeWrongByteCount)
• body, shape and joint ids stored to a 64-bit value and loaded back (IdTest)

The world at run time:

• world_set_worker_count and world_get_worker_count (TestSetWorkerCount)
• the per-colour contact counts in Counters (TestOverflowColorPile reads colorCounts[overflow])
• the SIMD width chosen at run time, where the reference forces 4 or 8 in one process (SIMDWidthTest); here it is a build choice (-mavx2) and solver.set_wide_contacts
• get_max_manifold_points (MaxPointCountTest)
• a name on ShapeDef, with the reference's truncation (ShapeNameTest)

Each should land with its reference subtest.