SendGrid Client, Memory Leaks, and IDisposable

[larlewis]

The BaseClient should implement the IDisposable interface as it contains a disposable HttpClient.
Internally, none of the references to HttpRequestMessage or HttpResponseMessage are properly disposed of, either in a using statement or explicitly.

This causes the underlying streams and sockets to hang around leading to memory leaks and socket exhaustion.

https://learn.microsoft.com/en-us/dotnet/fundamentals/runtime-libraries/system-idisposable

I'm not sure why this has been ignored, and for so long, but it has.