Give every test a bus of its own, at the release the mesh runs (hq ADR 0237)

The live tests reached one shared bus and assert, read and remove the mesh's own objects by
their fixed names, so packages run in parallel deleted what each other read and the suite
passed only one package at a time; a red suite read as noise. internal/testbus starts a server
per test, linked in at the nats-server release go.mod pins, and a test holds that pin to the
catalogue's bus image and to the facts snapshot's bus when there is one, so the tests never run
a bus the mesh does not. The waiter test read a timing (the most connections held at one look)
and now reads the state it means (the fewest held across the wait). make check runs the packages
in parallel under the race detector, with a timeout.

cmd/mesh-controller/doctor_test.go

@@ -5,7 +5,6 @@ import (
 	"encoding/json"
 	"errors"
 	"net"
-	"os"
 	"slices"
 	"strings"
 	"sync/atomic"
@@ -20,6 +19,8 @@ import (
 	"github.com/novox/mesh-controller/internal/catalogue"
 	"github.com/novox/mesh-controller/internal/conditions"
 	"github.com/novox/mesh-controller/internal/link"
+
+	"github.com/novox/mesh-controller/internal/testbus"
 )
 
 // The self-check (novox/hq to-be 45 §4): a probe that fails raises its condition, one that cannot run
@@ -250,10 +251,7 @@ func TestAResolverAnsweringNoSuchNameForIPv6IsWrong(t *testing.T) {
 // **D6, D7: what the controller defines is what it finds**, and a consumer deleted or a stream
 // redefined is said — against a real bus, raised by the same derivation the controller starts with.
 func TestNatsTheBusIsWhatTheControllerDefines(t *testing.T) {
-	url := os.Getenv("MESH_TEST_NATS")
-	if url == "" {
-		t.Skip("MESH_TEST_NATS unset")
-	}
+	url := testbus.URL(t)
 	open := aMesh(t)
 	js, err := broker.Dial(url)
 	if err != nil {
@@ -300,10 +298,7 @@ func TestNatsTheBusIsWhatTheControllerDefines(t *testing.T) {
 
 // **S9 hears the bus**: a consumer that gives up on a message, and one deleted, as the server says.
 func TestNatsTheBusSaysAConsumerGaveUpAndOneWasDeleted(t *testing.T) {
-	url := os.Getenv("MESH_TEST_NATS")
-	if url == "" {
-		t.Skip("MESH_TEST_NATS unset")
-	}
+	url := testbus.URL(t)
 	conn, err := nats.Connect(url)
 	if err != nil {
 		t.Fatal(err)