Description

This PR fixes two tessellation and morphology edge cases and makes the related tests deterministic:

• Handles fallback tessellation cells that coexist with multi-building cells without duplicating fallback place rows.
• Adds a retry path for degenerate enclosed tessellation recovery when the coarser grid_size retry fails during boundary simplification, falling back to simplify=False.
• Replaces the OSMnx downloaded graph smoke test with an in-memory MultiDiGraph fixture so the test no longer depends on live network data.
• Adds regression coverage for fallback building cells, tessellation simplification retry behavior, and the deterministic OSMnx-style graph conversion path.

Related Issues

NA

Checklist

• I have read the Contributing Guide.
• I have updated the documentation, if necessary.
• I have added tests to cover my changes.
• All new and existing tests passed.
• Pre-commit checks passed locally.