Function yarray_observe 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn yarray_observe(
    array: *const Branch,
    state: *mut c_void,
    cb: extern "C" fn(*mut c_void, *const YArrayEvent),
) -> *mut Subscription

Subscribes a given callback function cb to changes made by this YArray instance. Callbacks are triggered whenever a ytransaction_commit is called. Returns a subscription ID which can be then used to unsubscribe this callback by using yunobserve function.