RFR: 8364263: HttpClient: Improve encapsulation of ProxyServer

[Daniel Fuchs]

On Thu, 14 Aug 2025 18:33:51 GMT, Volkan Yazici <vyazici at openjdk.org> wrote:

> Make `ProxyServer` not extend from `Thread`.

LGTM. Please make sure to run all tests that might be using this class (tier2 should do it) to double check that none of them use methods from Thread - such as calling `proxy.join()`. With this change that would no longer compile.

-------------

PR Review: https://git.openjdk.org/jdk/pull/26786#pullrequestreview-3123484227