feat(analysis): type predicate subquery placeholders from columns

[omer-cengel]

Summary

Placeholders inside EXISTS, NOT EXISTS, [NOT] IN (SELECT ...), and scalar comparison subqueries are now typed and named from columns, so membership checks and correlated filters compile without casts. A predicate subquery is analyzed as a nested read that sees its own sources first and then each enclosing query's sources, as PostgreSQL resolves correlated references.

Changes

• Analyze predicate subqueries wherever the WHERE rules reach them through AND, OR, NOT, and parentheses: a read's WHERE, a join ON condition, an UPDATE or DELETE WHERE, an ON CONFLICT target predicate, a DO UPDATE predicate, and the WHERE of another analyzed nested query.
• Resolve columns through a scope chain: unqualified columns resolve in the innermost level that has them and are ambiguous only within one level; qualified columns use the innermost source of that name; a join condition sees only the sources up to its joined source. An unknown column names every visible source from the innermost level outward.
• Descend into NOT, so NOT (id = :id) types its placeholder.
• Put a write's WITH clauses in scope of the predicate subqueries of its WHERE and conflict predicates.
• Accept SELECT 1, wildcards, and columns of unmapped types in a predicate subquery's select list, while still rejecting an unknown direct column there; a set operation inside a predicate subquery gets the set-operation diagnostic.
• Keep binding order as the textual order of placeholders across all levels; a named placeholder repeated across levels is one parameter.
• Add analyzer tests for each form and location, generated-source compilation tests, and a PostgreSQL test of an uncast membership check and a correlated NOT EXISTS filter; update the query documentation.

Scope and non-goals

• = ANY (SELECT ...), IN ((SELECT ...)), a bare boolean subquery, and subqueries in a projection, GROUP BY, HAVING, ORDER BY, a written value, RETURNING, or a function argument keep their existing unanalyzed handling, where only a cast types a placeholder.
• A placeholder compared with a subquery, such as :x = (SELECT ...), is not typed from it.
• A WITH body or FROM subquery nested inside a predicate subquery still sees no enclosing source.
• Generated code structure, the runtime, and executable SQL are unchanged.