Function yarray_observe 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn yarray_observe(
    array: *const Branch,
    key_len: u32,
    key: *const c_char,
    state: *mut c_void,
    cb: extern "C" fn(*mut c_void, *const YArrayEvent),
)

Subscribes a given callback function cb under a key to changes made by this YArray instance. Callbacks are triggered whenever a ytransaction_commit is called. Use yunobserve with the same key to unsubscribe.