fix(executor): preserve SQL three-valued boolean logic [CODEX]

[dev-willbird1936]

Closes #7960.

The Python executor maps SQL boolean operators to Python truthiness, which makes NOT NULL evaluate as True instead of SQL UNKNOWN.

This patch adds SQL-aware NOT, AND, OR, and IN helpers. Lazy AND and OR operands preserve decisive short-circuit behavior, and boolean normalization keeps compatible scalar values working.

Regression tests cover nullable truth tables, nullable WHERE filtering, IN/NOT IN, NumPy boolean scalars, and evaluation count. The focused regressions, all 26 executor tests, Ruff, formatting, mypy, and git diff --check pass.

Disclosure: I used OpenAI Codex to assist with analysis and implementation. I reviewed and validated every submitted change.