additional safety condition for terminal rules

[hjyeob]

Currently ultk defines terminal rule as following:
if rhs and len(rhs) == 1 and issubclass(rhs[0], Referent):
This only allows rules with one Referent-like argument as a terminal rule.

• However, issubclass crashes when RHS annotation is a typing object (such as typing.Callable).
• Fixed this issue by checking inspect.isclass(rhs[0]) before calling issubclass.
• The main logic of terminal rule, one referent-like argument, remains unchanged.

Example (CRASP grammar NOT and COUNT):

def NOT(p: bool_op) -> bool_op:
    """Create a boolean operation that negates the result of another boolean operation.

    Args:
        p (bool_op): The boolean operation to negate.

    Returns:
        bool_op: A boolean operation function that performs negation and returns its truth value.
    """
    return lambda seq, idx: not p(seq, idx)

def COUNT(p: bool_op) -> count_op:
    """Create a count operation that counts how many positions up to index satisfy a predicate.

    Args:
        p (bool_op): The boolean operation (predicate) to count.

    Returns:
        count_op: A count operation function that applies given boolean operation at each index 
                  and returns the number of index where predicate holds true.
    """
    return lambda seq, idx: sum(p(seq, j) for j in range(min(idx + 1, len(seq))))

These functions will not be accepted as a valid grammar rule in current setting, but they should be accepted as non-terminal rule since their argument is another primitives.

[shanest]

Great! I see the issue you were encountering now, i.e. that issubclass would raise an error if rhs[0] was not a class. Thanks for uncovering and fixing