Add an in-process requester to responder handshake test

[aidangarske]

Context

The responder is exercised end to end only through wolfTPM's fwTPM e2e runs in the downstream job. A Codex review asked for a loopback test inside wolfSPDM.

Origin

main...wolftpm-core

What is needed

• Unit test that wires the requester I/O callback to wolfSPDM_ResponderProcess and runs identity-key and PSK handshakes, a secured vendor command, END_SESSION, and reconnect.

Blockers and dependencies

No response

Acceptance criteria

The test runs in make check for TCG + responder builds.