[simulation] add reliable virtual time transport (#11029)

This commit adds a reliable transport based on SEQPACKET unix socket to
simulation platform and use this for tests on simulation platform.

script/test

@@ -89,6 +89,9 @@ readonly TREL
 LOCAL_OTBR_DIR=${LOCAL_OTBR_DIR:-""}
 readonly LOCAL_OTBR_DIR
 
+: "${OT_VT_USE_UNIX_SOCKET:=0}"
+export OT_VT_USE_UNIX_SOCKET
+
 build_simulation()
 {
     local version="$1"