Handle unresolved JSON parameter types

[adsharma]

Summary

• serialize Python JSON parameters under to_json() only when they contain unresolved type shapes like empty lists, empty dicts, or nulls
• keep homogeneous arrays such as {"tags": [1, 2, 3]} on the normal typed binding path to avoid unnecessary stringify overhead
• add regression coverage for empty nested lists and for preserving typed binding on homogeneous lists

Root Cause

Persisting a Python dict through to_json() can bind nested empty lists as LIST. The engine rejects vectors with ANY because binding is expected to resolve concrete types before persistence.

Validation

• uv run pytest test/test_json.py -q
• uv run pytest test.py -q
• commit hooks: black, ruff check