test(charts): remove pyright suppressions from CLI tests

[tmustier]

Summary

Remove local pyright suppression pragmas from tests/test_charts_cli.py and make the test fakes/helpers strictly typed.

Changes

• Removed per-file pyright suppression header from tests/test_charts_cli.py
• Added typed helper _to_str_dict(...) for fake-engine spec normalization
• Tightened _chart_types(...) with explicit runtime guards to avoid unknown member access
• Updated _FakeEngine.normalize_chart_specs(...) to avoid unknown dict/list value propagation
• Preserved all existing test behavior and expectations

Validation

• .venv/bin/pyright tests/test_charts_cli.py
• .venv/bin/pytest -q tests/test_charts_cli.py
• .venv/bin/pre-commit run --all-files