feat(optimizer)!: Annotate LENGTH(expr) for DuckDB

[AbhishekASLK]

This PR annotate LENGTH(expr) for DuckDB

duckdb> select typeof(length('aslk'));
┌────────────────────────┐
│ typeof(length('aslk')) │
╞════════════════════════╡
│ BIGINT                 │
└────────────────────────┘

Official documentation:
https://duckdb.org/docs/stable/sql/functions/text#lengthstring