feat(raft-adapter-conformance): wire term-adoption into primary-side config-push reply handler

myreq_handler's ReplConfigPushReply branch now routes cack->term
through raft_on_higher_term_observed (same entry point the
heartbeat-reply and WAL-NACK vectors use), regardless of accept/reject,
without altering the existing accept/reject branching.

Adds myreq_handler_for_test (XCE_TESTING-only) to drive the real
dispatcher in tests, following the peer_ctrl_msg_handler_for_test
precedent. Requires cluster.c in controller_unit_test_src plus the
established link-satisfying fake stubs for its unrelated switch-case
dependencies (same pattern already used by test_worker_join.c and
test_commit_barrier_reply.c).

src/controller/meson.build

@@ -193,6 +193,7 @@ controller_unit_test_src = [
   'ctrl_metrics.c',
   'config_repl.c',
   'slowlane.c',
+  'cluster.c',
 ]
 
 ssl_dep = dependency('openssl')