feat(duckDB): Cast inputs (BLOB → VARCHAR) for duckDB STARTS_WITH

[fivetran-amrutabhimsenayachit]

When STARTS_WITH is used with BLOB/BYTES types that are not literals (e.g., from CAST, table columns, function results), the transpiled DuckDB query fails because DuckDB's starts_with only accepts VARCHAR.

Before:

sqlglot %  bq --project_id fivetran-wild-west query --use_legacy_sql=false "SELECT STARTS_WITH(CAST('foo' AS BYTES), CAST('f' AS BYTES))"                            
+------+
| f0_  |
+------+
| true |
+------+
sqlglot % python3 -c "import sqlglot; print(sqlglot.transpile(\"SELECT STARTS_WITH(CAST('foo' AS BYTES), CAST('f' AS BYTES))\", read='bigquery', write='duckdb')[0])"
SELECT STARTS_WITH(CAST('foo' AS BLOB), CAST('f' AS BLOB))

sqlglot % duckdb -c "SELECT STARTS_WITH(CAST('foo' AS BLOB), CAST('f' AS BLOB))"                                                         
Binder Error:
No function matches the given name and argument types 'starts_with(BLOB, BLOB)'. You might need to add explicit type casts.
        Candidate functions:
        starts_with(VARCHAR, VARCHAR) -> BOOLEAN


LINE 1: SELECT STARTS_WITH(CAST('foo' AS BLOB), CAST('f' AS BLOB))

After:

sqlglot % bq --project_id fivetran-wild-west query --use_legacy_sql=false "SELECT STARTS_WITH(CAST('foo' AS BYTES), CAST('f' AS BYTES))"     
+------+
| f0_  |
+------+
| true |
+------+
sqlglot % python3 -c "import sqlglot; print(sqlglot.transpile(\"SELECT STARTS_WITH(CAST('foo' AS BYTES), CAST('f' AS BYTES))\", read='bigquery', write='duckdb')[0])"
SELECT STARTS_WITH(CAST(CAST('foo' AS BLOB) AS TEXT), CAST(CAST('f' AS BLOB) AS TEXT))

sqlglot % duckdb -c "SELECT STARTS_WITH(CAST(CAST('foo' AS BLOB) AS TEXT), CAST(CAST('f' AS BLOB) AS TEXT))"
┌───────────────────────────────────────────────────────────────────────┐
│ starts_with(CAST('foo'::BLOB AS VARCHAR), CAST('f'::BLOB AS VARCHAR)) │
│                                boolean                                │
├───────────────────────────────────────────────────────────────────────┤
│ true                                                                  │
└───────────────────────────────────────────────────────────────────────┘

[georgesittas]

This path is not tested– moreover, I don't think it's correct.

[georgesittas]

Can we do if not is_type(VARCHAR, UNKNOWN): ... instead? Check out my comment in Tori's PR.