Track scope for CTEs to fix ambiguous column bug - #1

sqlc does not track scope for CTEs. A subquery inside a CTE makes column references in the CTE, and in CTEs that select from it, resolve against the subquery's tables too, so valid queries fail to generate:

query.sql:11:20: column reference "owner_id" is ambiguous
query.sql:24:20: column "w_owner_id" does not exist
query.sql:38:20: column reference "owner_id" is ambiguous

A minimal shape that triggers it:

WITH cte AS (
	SELECT owner_id
	FROM table_with_owner_id
	WHERE EXISTS (SELECT 1 FROM another_table_with_owner_id)
)
SELECT * FROM cte;

This change tracks the CTE a column reference belongs to when resolving columns and parameters. The new cte_ambiguous_column testdata reproduces the errors above. Parameters inside a CTE, or compared against a CTE column, now get the referenced type instead of a nullable fallback: cte_left_join generates name string (was dollar_1 pgtype.Text), and cte_update generates bool, string, int64 (was pgtype.Bool, pgtype.Text, pgtype.Int8).

main never had this fix. The fork was pinned to the side branch mafredri/fix-ambiguous-column.import, and #6 merged upstream v1.31.1 into main without it. This branch is the fix applied to main (337309bf), with the new testdata regenerated for the v1.31.1 version stamp.

go test ./... against PostgreSQL 16 fails the same tests on main and on this branch: TestReplay/{base,managed-db}/wasm_plugin_sqlc_gen_unsafe_paths. Its expected error path depends on where the repository is checked out.

Upstream: sqlc-dev#4159

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