PollingApiProposal.cs

// doesn't block
void StartReceiving(Func<Update, Task> updateHandler, Func<Exception, Task> exceptionHandler);

// awaitable blocking task
async Task ReceiveAsync(Func<Update, Task> updateHandler, Func<Exception, Task>? exceptionHandler);

// calls GetUpdates after all updates are processed
async IAsyncEnumerable<Update> YieldUpdatesAsync(Func<Exception, Task>? exceptionHandler);

// keeps calling GetUpdates and enqueues updates internally, yielding them one by one
// implementation and different variants TBD
async IAsyncEnumerable<Update> YieldQueuedUpdatesAsync(Func<Exception, Task>? exceptionHandler);

// All variants also have optional `UpdateType[]?` and `CancellationToken` parameters.
// `exceptionHandler` is optional, except on `StartReceiving`.