feat(duckdb): cast LOWER() result to BLOB if input is bytes

[toriwei]

BigQuery's LOWER() can accept and return BYTES. DuckDB's LOWER() works withBYTES but returns VARCHAR. This PR casts result of LOWER() to BLOB for more accurate transpilation.

BigQuery
SELECT LOWER(b'\x41\x42\x43') as example, TYPEOF(LOWER(b'\x41\x42\x43')) as example_type

+---------+--------------+
| example | example_type |
+---------+--------------+
|    YWJj | BYTES        |
+---------+--------------+

DuckDB before changes:

D SELECT LOWER(e'\x41\x42\x43') as example;
┌─────────┐
│ example │
│ varchar │
├─────────┤
│ abc     │
└─────────┘

DuckDB with updated casting:

D SELECT CAST(LOWER(e'\x41\x42\x43') AS BLOB) as example;
┌─────────┐
│ example │
│  blob   │
├─────────┤
│ abc     │
└─────────┘