fix(database): prevent deeply nested has many map adding extra empty object

[nunntom]

closes #1994

• Added failing assertion to existing test showing the bug
• Removed line in SelectModelMapper that adds initial empty model. It doesn't seem necessary since the later $data->set adds the full nested path anyway. Please correct me if I'm wrong or if I broke anything. Tests are all still passing (including the failing one I added).

[github-actions]

Benchmark Results

Comparison of deeply-nested-has-many-map-bug against 3.x (5563eac1332581f39b908f0e4b23adf53167c282).

Open to see the benchmark results

Benchmark	Set	Mem. Peak	Time	Variability
ViewRenderBench(benchPlainHtml)	-	21.481mb 0.00%	488.857μs -5.87%	±3.67% +27.95%

_{Generated by phpbench against commit 7c8dee2}