stevehansen
Support for `TextWriter.WriteAsync`
When writing to the TextWriter there is both are both synchronous (.Write) and asynchronous (.WriteAsync) methods. Its not hard to imagine situations where this maters, but in particular when I'm writing to the context for ASP.NET Core it only supports writing with the Async versions. As is that makes this library almost unusable for serializing HTTP responses.
I propose making the Async versions of the calls use the WriteAsync methods where possible. I'm able to implement most of the change but the WriteCellMemory function takes in a ReadOnlySpan which can't be passed to an async method. The other thing I didn't do in my implementation was handle cancellation tokens properly. I'm not sure how important that is but it's something to look at.
