* Move mockServer into a separate file.
* Refactor mock server and client test.
* Use mTLS in client tests.
* Move mtls test helpers into a new package for reusability.
* Fix an issue ALPN handshake test does not respect "HTTPS_PROXY"
* address review comment
* remove simplehttsproxy
* Add context to IsALPNConnUpgradeRequired in ten thousand places
* add goc and dial with context