onCompletion callbacks are invoked if complete() or fail() is called before the stream is disposed.
onDisposal callbacks are invoked if the stream is disposed before being completed or failed.
Forbid failing a stream with DisposedException.
A suggested alternative to resolving with [$yieldedValue] since static analysis (specifically Psalm) doesn't play well with that API.
Will revert if Psalm changes or we decide to resolve with [$yieldedValue] anyway.