fix: filter out NaN vertices from IFC geometry

[TeapoyY]

Summary

When loading certain IFC files, the web-ifc parser can produce geometry with NaN position values. This causes Three.js to throw computeBoundingSphere(): Computed radius is NaN when the geometry's bounding sphere is computed, crashing the application.

This fix adds a NaN check in ifcGeometryToBuffer():

1. First pass: identify vertices with NaN position coordinates
2. Fast path: if all vertices are valid (no NaN), use the original code unchanged — zero overhead for well-formed files
3. Slow path: if NaN vertices are found, filter them out and remap the index buffer to exclude any triangles that reference invalid vertices

The Bug

Issue: #88

When loading an IFC file with malformed geometry data (e.g., from ifc2.zip attached to the issue), the vertex positions contain NaN values. When Three.js tries to compute the bounding sphere for rendering, it gets NaN for the radius and throws an uncaught error.

The Fix

In IFCParser.ifcGeometryToBuffer(), after extracting the vertex data from web-ifc:

• Check each vertex's (x, y, z) position values using Number.isFinite()
• Build a validity flag array and count of valid vertices
• If all valid: use the original code unchanged
• If any invalid: build a remapping from old vertex indices to new compact indices, construct new compact position/normal/id arrays, and a new index buffer that only references valid vertices (dropping degenerate triangles)

Bounty

This PR addresses #88 (labeled: bounty)