Deserialize from from Stream instead of from String

[MrSmoke]

Change BaseRestClientRequest to deserialize the content using a stream and pass that stream to a new method on Serializer which accepts a Stream.

• Added new ValueTask<T?> DeserializeAsync<T>(Stream, CancellationToken); to ISerializer
  • Uses Task for full fat .net
• When calling HttpClient.SendAsync, use HttpCompletionOption.ResponseHeadersRead to avoid buffering the response internally
• Update NewtonsoftJsonSerializer to use a single instead of JsonSerializer instead of the JsonConvert methods
  • I basically copied how the JsonConvert methods work

Some benchmarks showing the lower memory usage

Old:

 Method       | Mean     | Error     | StdDev    | Gen0     | Gen1     | Gen2    | Allocated |
|------------- |---------:|----------:|----------:|---------:|---------:|--------:|----------:|
| ExecuteAsync | 1.588 ms | 0.0316 ms | 0.0519 ms | 146.4844 | 109.3750 | 72.2656 | 951.09 KB |

New:

| Method       | Mean     | Error     | StdDev    | Gen0     | Gen1    | Gen2    | Allocated |
|------------- |---------:|----------:|----------:|---------:|--------:|--------:|----------:|
| ExecuteAsync | 1.503 ms | 0.0299 ms | 0.0508 ms | 109.3750 | 35.1563 | 35.1563 |  781.8 KB |