Batch Support for AxisAlignedBoundingBox

[zhx06]

Summary

Add batch dimension support to AxisAlignedBoundingBox

Detailed description

• What was the reason for the change?
  • To support multi-environment batched placement, AxisAlignedBoundingBox needs to handle N bounding boxes simultaneously instead of only one.
• What has been changed?
  • Refactored AxisAlignedBoundingBox from a dataclass to a class with (N, 3) float32 tensor storage. Returns tuples/floats for N=1, tensors for N>1.
  • Fixed float32 rounding issue in _validate_on_relations Z boundary check.
  • Added test_bounding_box.py for single-env and multi-env coverage.
• What is the impact of this change?
  • No behavior change for existing code: backward compatible for single env (N=1).
  • Enables future multi-env batch support for the coming relation solver MR.