feat: add DuckDB dialect support

[adamatmotherduck]

Summary

Adds a complete DuckDB SQL dialect to node-sql-parser, enabling parsing and SQL generation for DuckDB-specific syntax. This has been a highly requested feature (13 upvotes).

• New grammar: pegjs/duckdb.pegjs (based on PostgreSQL grammar with extensive DuckDB-specific additions)
• 107 new tests in test/duckdb.spec.js covering all added features
• Minimal changes to shared src/ files (56 lines added across 8 files) with zero regressions to existing 1515 tests

DuckDB-specific syntax supported

Feature	Example
:: type casts (incl. array)	val::INTEGER, arr::DATE[]
QUALIFY clause	SELECT ... QUALIFY ROW_NUMBER() OVER (...) = 1
GROUP BY ALL / ORDER BY ALL	SELECT col, SUM(x) FROM t GROUP BY ALL
EXCLUDE / REPLACE	SELECT * EXCLUDE (col) REPLACE (expr AS col)
PIVOT / UNPIVOT	FROM t PIVOT (SUM(x) FOR col IN ('a', 'b'))
Lambda expressions	list_transform(arr, x -> x + 1)
Struct / list literals	{'key': value}, [1, 2, 3]
COLUMNS() expression	SELECT COLUMNS('pattern.*') FROM t
UNION BY NAME	SELECT * FROM t1 UNION BY NAME SELECT * FROM t2
ASOF / SEMI / ANTI / POSITIONAL JOIN	FROM t1 ASOF JOIN t2 ON ...
INSERT BY NAME	INSERT INTO t BY NAME SELECT * FROM src
INSERT OR REPLACE / IGNORE	INSERT OR REPLACE INTO t ...
IS NOT DISTINCT FROM	t1.col IS NOT DISTINCT FROM t2.col
CREATE OR REPLACE TABLE	CREATE OR REPLACE TABLE t AS SELECT ...
COPY with subquery	COPY (SELECT ...) TO 'file.parquet' (FORMAT PARQUET)
FROM-first queries	FROM t WHERE x > 1 LIMIT 10
DESCRIBE / SUMMARIZE	SUMMARIZE my_table
ATTACH / DETACH	ATTACH 'db.duckdb' AS mydb
DuckDB types	HUGEINT, UBIGINT, BLOB, STRUCT, MAP, LIST, UNION
PARTITION BY tuple	PARTITION BY (col1, col2)

Files changed

File	Change
pegjs/duckdb.pegjs	New — DuckDB grammar (182KB)
test/duckdb.spec.js	New — 107 tests incl. real-world query patterns
src/parser.all.js	Add duckdb import
src/util.js	Add duckdb to double-quote identifier list
src/column.js	Handle EXCLUDE+REPLACE combo columns
src/create.js	Handle OR REPLACE for DuckDB CREATE
src/expr.js	Add struct_value serialization
src/insert.js	Add BY NAME support
src/sql.js	Register new statement types
src/union.js	Add summarize/detach/copy SQL generation

Test plan

• All 107 new DuckDB tests pass
• All 1515 existing tests pass (zero regressions)
• npm run build succeeds
• Grammar size (182KB) is comparable to PostgreSQL (171KB)

Closes #1944

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