fix(search): Preserve grouped aggregate filter values (#123037)

Grouped search queries now preserve their closing boolean-group
delimiter when the final filter uses an aggregate function key. The
legacy tokenizer balances unquoted parentheses, preventing comparison
values from absorbing the group delimiter and being rewritten as quoted
strings.

Quote scanning now also uses odd/even backslash parity consistently
across token splitting, filter parsing, and serialization. This
preserves grouping when a quoted filter value ends in a literal
backslash while leaving legitimate parenthesized values unchanged.