Stream Overture building stats by batch

[mividtim]

Summary:

• add a streaming Overture building-batch path for parcel building stats
• use the streaming path from Overture enrichment so dense bboxes do not materialize every footprint at once
• keep get_buildings compatible for existing callers
• add old-vs-streaming equivalence tests for footprint area, max height, max floors, empty inputs, and no-height inputs

Verification:

• focused Overture pytest in the AVM worker venv: 6 passed
• git diff --check: clean

Note: a broader local tests/test_data.py run is blocked in the reused AVM worker venv by missing ngboost; the focused Overture tests run in the same geospatial dependency stack used by the AVM worker.

[github-actions]

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