Flurl Extensions for Downloading Binary Data for easy Deferred streaming as AsyncEnumerable streams.

FlurlDownloadAsAsyncEnumerableExtensions.cs

//WIP: This is an extension method for Flurl to download a Binary file direcctly into an AsyncEnumerable that that 
//      can then be iterated with deferred execution for streaming binary data without downloading all data into Memory  OR
//      needing to store in an intermediate location.

//TODO:
// - Implement IAsyncEnumerable wrapper for the Stream Reading which can then be easily chunked via Linq just as it currently is...
// - This method may run a quick HTTP GET for headers Only to check and confirm existence, and then return an AsynEnumerable wrapper with an internal Delegate that creates the Stream
//      reads the bytes in buffer/chunk sizes until Zero bytes are read; this would occur inside the GetEnumerator() call...
// - Develop this as an Open Source (e.g. Gist) Flurl Extension method for Re-use and sharing!
// - Reference Flurl's DownloadFileAsync for getting a true Async stream (would happen in the Delegate when IAsyncEnumerable.GetEnumerator() is called...