fix#3874 (http-support): make NewHttpClientImpl.execute non-blocking

[YianZhao]

Implemented a fix for the native HTTP client async contract in NewHttpClientImpl.execute().

• Removed blocking behavior (sendAsync(...).get()) and replaced it with a non-blocking async chain.
• execute() now returns immediately and completes the returned CompletableFuture when the HTTP response arrives.
• Preserved exception propagation from ResponseProcessor in async completion flow.
• Added dedicated unit tests for non-blocking behavior and processor exception path.

Issue: #3874

No new dependencies were added or updated.

Suggest Reviewer

@GMishx

How To Test?

1. Run:

   mvn -pl clients/http-support "-Dbase.deploy.dir=." "-DskipTests=false" "-Dmaven.test.skip=false" "-Dtest=NewHttpClientImplTest,HttpClientImplTest" test