[python][ray] Fix count metadata for row-level authorization

[QuakeWang]

Purpose

RayDatasource falls back to physical row counts when logical counts are unknown. This can make Ray count() return unfiltered counts for tables with row-level authorization.

Preserve unknown counts as None and retain exact zero counts, so Ray counts filtered output when necessary.

Tests

• 88 tests passed across ray_integration_test.py, ray_data_test.py, and table_query_auth_test.py on Ray 2.54.0.
• All 8 reproduction and control scenarios passed.
• Python Flake8, license checks, and git diff --check passed.

[XiaoHongbo-Hope]

+1