feat: type query placeholders by their SQL cast

[omer-cengel]

Summary

Lets a query state a placeholder's type with a cast, so common idioms such as an optional filter (:name::text IS NULL OR name = :name), a computed pattern '%' || :term::text || '%', and SET bio = COALESCE(:bio::text, bio) compile as written. The cast type is resolved by the same declared-type mapping the schema parser uses, now extracted into a shared ColumnTypeMapping.

Changes

• A $N or :name placeholder that is the direct operand of ::type or CAST(... AS type) anywhere inside WHERE, an INSERT value, or an UPDATE assignment takes the cast's type, including declared enums, char(n), and one-dimensional arrays such as tags && $1::varchar[].
• A named cast placeholder keeps its own name. An indexed one keeps the column name an uncast placeholder would take in that position (compared, IN, BETWEEN, plain LIKE/ILIKE pattern, inserted, or assigned column), and is otherwise named param<N>. A cast pattern under NOT LIKE, SIMILAR TO, ESCAPE, or BINARY is accepted and named param<N>.
• Occurrences of one placeholder may mix cast and uncast locations; conflicting types are rejected.
• Rejected with diagnostics: an unmapped cast type such as $1::interval or $1::int[][], a cast placeholder in an unanalyzed location such as ORDER BY $1::int, a placeholder that is not the cast's direct operand, and quoted, qualified, or &name cast operands, which previously reached the executable SQL unreplaced.
• The declared SQL type mapping moves from DefaultSchemaParser into ColumnTypeMapping without changing schema parsing.
• Query documentation describes the accepted casts, naming, and rejections, with analyzer, compiler, generated-code, and PostgreSQL execution tests.

Scope and non-goals

• Casts in projections, ORDER BY, HAVING, join conditions, pagination values, and subqueries stay rejected; computed or cast projections are not added.
• The uncast LIKE pattern restrictions and their messages are unchanged, as are queries without casts.
• Code generation and the runtime are unchanged.