fix(optimizer): preserve negated correlations [CODEX]

[dev-willbird1936]

Closes #7958.

A direct NOT around a correlated comparison was lost during decorrelation because the inner comparison was replaced with TRUE. This change normalizes supported direct negated comparisons to their complementary operator, aggregates the inner key when no positive equality join key exists, and evaluates the preserved predicate with ARRAY_ANY after a LEFT JOIN ... ON TRUE.

The regression covers EXISTS, NOT EXISTS, the existing positive-equality path, NULL/UNKNOWN values, an all-NULL inner relation, and an empty inner relation.

Validation:

• focused optimizer and executor regressions
• full executor suite: 22 passed
• relevant unnest_subqueries optimizer fixture plus regression
• Ruff check and format
• mypy over 180 source files
• git diff --check

LLM disclosure: I used OpenAI Codex to assist with analysis, implementation, and test drafting. I reviewed the final diff and validated the behavior and tests.