Native replace() returns wrong result for empty-string search

Description

Comet's native replace() function returns incorrect results when the search string is empty.

Spark behavior: replace('hello', '', 'x') returns xhxexlxlxox (inserts replacement between every character and at boundaries).

Comet behavior: returns hello (no replacement).

SELECT replace('hello', '', 'x');

Expected: xhxexlxlxox
Actual (Comet): hello

Comet should match Spark's semantics for empty-string search in replace().

Add literal argument tests for all SQL file expression tests

take

@wattt3

@wattt3 apologies - this issue seems to be invalid. It is based on the behavior of Java's string replace method and not the Spark implementation

chore(audit): address PR review feedback on string-expressions audit