feat(duckdb): Add transpilation support for HEX_DECODE_STRING

[fivetran-amrutabhimsenayachit]

HEX_DECODE_STRING is not transpiled; passes through unchanged, DuckDB has no such function (Catalog Error on all inputs)

[github-actions]

SQLGlot Integration Test Results

Comparing:

• this branch (sqlglot:RD-1147719-hex-decode-string, sqlglot version: RD-1147719-hex-decode-string)
• baseline (main, sqlglot version: 0.0.1.dev1)

By Dialect

dialect	main	sqlglot:RD-1147719-hex-decode-string	transitions	links
bigquery -> bigquery	24647/24652 passed (100.0%)	23497/23497 passed (100.0%)	No change	full result / delta
bigquery -> duckdb	867/1154 passed (75.1%)	0/0 passed (0.0%)	Results not found	full result / delta
duckdb -> duckdb	5823/5823 passed (100.0%)	5823/5823 passed (100.0%)	No change	full result / delta
snowflake -> duckdb	1120/1935 passed (57.9%)	1122/1935 passed (58.0%)	2 fail -> pass	full result / delta
snowflake -> snowflake	65133/65133 passed (100.0%)	65133/65133 passed (100.0%)	No change	full result / delta
databricks -> databricks	1370/1370 passed (100.0%)	1370/1370 passed (100.0%)	No change	full result / delta
postgres -> postgres	6042/6042 passed (100.0%)	6042/6042 passed (100.0%)	No change	full result / delta
redshift -> redshift	7101/7101 passed (100.0%)	7101/7101 passed (100.0%)	No change	full result / delta

Overall

main: 113210 total, 112103 passed (pass rate: 99.0%), sqlglot version: 0.0.1.dev1

sqlglot:RD-1147719-hex-decode-string: 110901 total, 110088 passed (pass rate: 99.3%), sqlglot version: RD-1147719-hex-decode-string

Transitions:
2 fail -> pass

Dialect pair changes: 0 previous results not found, 1 current results not found

✅ 39 test(s) passed