Function register_callback 

pub fn register_callback<F>(name: &str, f: F) -> Result<(), FfiError>
where
    F: Fn(FfiBuffer) -> FfiResult + Send + Sync + 'static,

Register a named callback from Rust code.

The closure receives an FfiBuffer input and must return an FfiResult.

Thread safety

This function acquires the global callback registry lock. Returns Err if the lock is poisoned.