Fix Primitive.indices to use uint32 indices instead of float32

[DHasper]

Problem

The Primitive.indices setter cast face indices to dtype np.float32. A 32-bit float has a 24-bit mantissa, so it can only represent integers up to 2^24 = 16,777,216. Index values above that get rounded to the nearest representable float, corrupting mesh topology on large meshes.

Fix

Primitive.indices dtype: use uint32 instead of float32