len of generic array causing InternalGuppyError

[ss2165]

example:

@guppy
@no_type_check
def array_any(arr: array[bool, n]) -> bool:
    for i in range(len(arr)):
        if arr[i]:
            return True
    return False

throws

    @staticmethod
    def _get_const_len(inst: Inst) -> ast.expr:
        """Helper function to extract the static length from the inferred type args."""
        # TODO: This will stop working once we allow generic function defs. Then, the
        #  argument could also just be variable instead of a concrete number.
        match inst:
            case [_, ConstArg(const=ConstValue(value=int(n)))]:
                return ast.Constant(value=n)
>       raise InternalGuppyError(f"array.__len__: Invalid instantiation: {inst}")
E       guppylang.error.InternalGuppyError: array.__len__: Invalid instantiation: [TypeArg(ty=OpaqueType(args=[], defn=OpaqueTypeDef(id=DefId(id=3, module=None), name='bool', defined_at=None, description='type', params=[], never_copyable=False, never_droppable=False, to_hugr=<function <lambda> at 0x106ccae80>, bound=None))), ConstArg(const=BoundConstVar(ty=NumericType(kind=<Kind.Nat: 1>), display_name='n', idx=0))]

using range(n) instead works, but I believe this is a regression.