pub fn new_owned(callable: Zval) -> Result<Self> {
        if callable.is_callable() {
            Ok(Self(OwnedZval::Owned(callable)))
        } else {
            Err(Error::Callable)
        }
    }
Attempts to create a new [`ZendCallable`] by taking ownership of a Zval.
Returns a result containing the callable if the zval was callable.

# Parameters

* `callable` - The underlying [`Zval`] that is callable.

# Errors

* [`Error::Callable`] - If the zval was not callable.
src/types/callable.rs