v0.3.0 - Batch Build API

Added

• BIMFactoryElement.build_in() — build many elements and assign them to a spatial
  structure in one batched call (IfcRelContainedInSpatialStructure or
  IfcRelAggregates). O(n) instead of O(n²) when placing large element sets
  (trees, terrain meshes, city models).
• BIMFactoryElement.batch_quantify() — run ifc5d quantity calculation once
  for all physical products instead of per element.
• HalfSpace primitive for geometry clipping.
• Deferred layer assignment via apply_layers() — presentation layers are
  accumulated during build_in() and written in a single pass.
• Examples 9 & 10 — IFC building model and IfcOpenHouse tutorials demonstrating
  batch build, type caching, and storey workflows.
• RGB normalization for Material and Style classes.

Improved

• Transform — optimized vertex transformation and rotation handling.
• IFC4 schema — cached at import time instead of fetched per element.
• Layer assignment in material_base.py — supports batch path used by build_in().

Fixed

• Material color — blue channel now read from rgb[2] instead of rgb[1].