fix: fix nested block reference osnap transforms and insertion points

[mlightcad]

PR Description

Summary

• Correct object snap resolution in AcDbBlockReference by propagating cumulative insertion transforms through nested block references.
• Transform pick/last points into block-local space before querying sub-entity osnap points.
• Return insertion snap points in world space using block base point + full insertion transform.
• Add regression tests for transformed pick-point snapping and nested block-reference osnap traversal.

Why

• Osnap queries against sub-entities in transformed/nested block references could return incorrect coordinates because world/local transforms were not consistently applied.
• Insertion osnap behavior needed to honor parent insertion context and block origin in nested scenarios.

What Changed

• Extended subGetOsnapPoints(...) with an optional cumulative insertionMat parameter.
• Reworked subEntityGetOsnapPoints(...) to:
• Track visited block references to prevent recursion loops.
• Build cumulative transforms per nesting level.
• Query sub-entities in local space and map results back to world space correctly.
• Added helpers for insertion-point and full insertion-transform computation.
• Updated base AcDbEntity.subGetOsnapPoints(...) signature/docs to include the optional insertion matrix.
• Added tests in AcDbBlockReference.spec.ts for:
• Pick-point transformation before nearest osnap query.
• End-point osnap resolution through nested block references.

Testing

• Added/updated unit tests in packages/data-model/__tests__/AcDbBlockReference.spec.ts
• Not run (drafted from git diff context only)

Risks / Notes

• Method signature change (subGetOsnapPoints adds optional parameter) is backward-compatible at call sites but may require attention for custom overrides/implementations.
• Nested traversal now depends on recursion with visited-set guards; edge cases with unusual reference graphs should continue to be monitored.