ASync 3 client upgrade, removal of stream / oauth feature

[Nezisi]

Follow up to #916

It's mostly a rebase + reformat I had from testing in Nov / 2024 .

Threw scalafmt on it and had a quick check of my notes / review.

Summary:

• removal of streaming feature
• removal of oauth feature
• to keep API intact: calc / signature methods were left as is
• javaDuration change: "-1" to "java.time.Duration.ZERO", see https://github.com/AsyncHttpClient/async-http-client/blob/0ebfd642b4b1c83d3c14febebb935a4f7e6729d9/client/src/main/java/org/asynchttpclient/DefaultRequest.java#L115
• StandaloneAhcWSRequest.scala: Removal of the SourceBody handling is another thing I'm not really sure if "correct" or "wrong" - it evaluates to a stream, stream got removed => but is it entirely stream related or could sth else utilize that code path?

@mkurz I still had the modifications, but I haven't thoroughly examined or tested them. Hope it helps 👍