feat: add GoogleSQL support to sqlc parse

[kyleconroy]

Adds a googlesql dialect to sqlc parse, backed by github.com/sqlc-dev/zetajones — a pure-Go (no cgo) GoogleSQL/ZetaSQL parser that passes the entire upstream google/googlesql parser golden-test corpus (~4,700 cases, byte-for-byte including error messages and caret positions).

sqlc parse --dialect googlesql queries.sql
echo "SELECT id FROM users WHERE status = @status" | sqlc parse --dialect googlesql

Structure

Follows the ClickHouse integration (#4267) exactly. New files in internal/engine/googlesql/:

• parse.go — Parser implementation using zetajones
• convert.go — AST converter from zetajones to sqlc AST
• utils.go — helpers (identifiers, string-literal unquoting, type rendering)
• catalog.go, stdlib.go — catalog initialization
• reserved.go — reserved keywords (delegates to zetajones/token)

Coverage

• Queries: SELECT list (aliases, *, expr.*), FROM (dotted table paths, JOINs, table subqueries incl. LATERAL, TVFs, UNNEST), WHERE, GROUP BY, HAVING, DISTINCT, ORDER BY, LIMIT/OFFSET, WITH/CTEs (incl. RECURSIVE), set operations
• DML: INSERT (VALUES + SELECT forms), UPDATE, DELETE — all incl. THEN RETURN → ReturningList
• DDL: CREATE TABLE (types, NOT NULL, PRIMARY KEY, type params, DEFAULT), DROP TABLE, TRUNCATE
• Expressions: literals, paths, boolean logic, BETWEEN/IN/IS NULL, CASE, CAST, subqueries (EXISTS/ARRAY/scalar), function calls incl. COUNT(*) and window functions, array subscripts

Design notes:

• Named parameters (@name) convert to the same A_Expr{"@"} shape the PostgreSQL and SQLite engines produce, so rewrite.NamedParameters consumes them unchanged. Positional ? → numbered ParamRef.
• Identifiers pass through case-sensitively (BigQuery table names are case-sensitive); function/type names, which GoogleSQL treats case-insensitively, are lowercased.
• Unsupported constructs (graph queries, scripts, pipe operators, MATCH_RECOGNIZE) convert to ast.TODO without panicking — the underlying parser is fuzz-tested (12M+ executions, no panics).

Testing

• go build ./..., go vet, gofmt clean; go test ./internal/engine/... ./internal/cmd/... ./internal/sql/... all pass
• Smoke battery over SELECT/JOIN/CREATE/INSERT/UPDATE/DELETE produces fully-populated ASTs (no TODOs), and unsupported statements exit cleanly

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