static Optional<Pair<FunctionReference, String>> fromTypeArgumentSerial(String serialForm) {
        Matcher expressionMatcher = argumentTypePattern.matcher(serialForm);
        if ( ! expressionMatcher.matches()) return Optional.empty();

        String name = expressionMatcher.group(1);
        String instance = expressionMatcher.group(2);
        String argument = expressionMatcher.group(3);
        return Optional.of(new Pair<>(new FunctionReference(name, instance), argument));
    }
Returns a function reference and argument name string from the given serial form,
or empty if the string is not a valid function argument serial form
model-evaluation/src/main/java/ai/vespa/models/evaluation/FunctionReference.java