fix(IfcImporter): add vertex key to geometry dedup hash

[ShaMan123]

Description

closes #237

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following:

• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Follow the Conventional Commits v1.0.0 standard for PR naming (e.g. feat(examples): add hello-world example).
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[ShaMan123]

The issue references an concise ifc repro fixture that can be used as a test case (once vitest is in)

[ShaMan123]

The vertex key construction is Claude's suggestion.

[ShaMan123]

Actually I am not sure this is a correct fix.
This doesn't cover cases that are geometrically the same with differently ordered vertices.

[agviegas]

Great repro, it makes the problem obvious: both plates share outline, area, volume and centroid, and the only difference is where the holes sit, which is exactly what the old key never looked at.

Direction is right. One thing to fix first: the vertexKey sum can cancel. JS % keeps the sign of the dividend, so h goes negative for negative coordinates and stays signed through the mixing. Summed commutatively, two vertices whose hashes are exact negatives cancel to zero and drop out of the key. The final if (vertexKey < 0) only fixes the sign of the result, not the cancellation. Normalize each h first:

let h = Math.round(position[i] * p) % MODULUS;
if (h < 0) h += MODULUS;

And a question: does the key need to be order-invariant at all? The commutative sum buys a match on a permuted buffer but costs collision resistance, where an ordered polynomial hash is stronger and simpler. Do we actually see web-ifc emit permuted duplicates? If not, I'd take the ordered one.

Minor: the AABB doesn't separate your two plates (same outline, same box), so vertexKey is carrying the fix alone. Fine to keep the corners, just noting what's load-bearing.

The #237 repro would make a good regression test. Still a draft, what's left on your side?