Timestamp conversion performance can be improved

executor.reduce(rexBuilder, ImmutableList.of(e), reducedValues);

if (typeName == SqlTypeName.CHAR && e.getType().getSqlTypeName() == SqlTypeName.TIMESTAMP_WITH_LOCAL_TIME_ZONE) {
    if (literal.getValue() instanceof NlsString) {
        String timestampStr = ((NlsString) literal.getValue()).getValue();
        Long timestampLong = SqlFunctions.toTimestampWithLocalTimeZone(timestampStr);
        reducedValues.add(rexBuilder.makeLiteral(timestampLong, e.getType(), true));
    }
}

if (reducedValues.isEmpty()) {
    executor.reduce(rexBuilder, ImmutableList.of(e), reducedValues);
}