Unify csimulator error handling

[wshlavacek]

Summary

• Replace ad hoc csimulator print and debug paths with structured errors and logger calls.
• Add focused regression coverage for invalid model input, wrapper initialization failures, and unresolved species counts.

Testing

• uv run python -m pytest -q tests/test_csimulator_errors.py
• uvx black --check bionetgen/core/exc.py bionetgen/simulator/csimulator.py tests/test_csimulator_errors.py