all: unify some redundant testing.TB interface copies

I added yet another one in 6d117d64a2 but that new one is at the
best place int he dependency graph and has the best name, so let's use
that one for everything possible.

types/lazy can't use it for circular dependency reasons, so unexport
that copy at least.

Updates #cleanup

Change-Id: I25db6b6a0d81dbb8e89a0a9080c7f15cbf7aa770
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

util/syspolicy/internal/metrics/metrics.go

@@ -259,7 +259,7 @@ var addMetricTestHook, setMetricTestHook syncs.AtomicValue[metricFn]
 
 // SetHooksForTest sets the specified addMetric and setMetric functions
 // as the metric functions for the duration of tb and all its subtests.
-func SetHooksForTest(tb internal.TB, addMetric, setMetric metricFn) {
+func SetHooksForTest(tb testenv.TB, addMetric, setMetric metricFn) {
 	oldAddMetric := addMetricTestHook.Swap(addMetric)
 	oldSetMetric := setMetricTestHook.Swap(setMetric)
 	tb.Cleanup(func() {

util/syspolicy/internal/metrics/test_handler.go

@@ -9,6 +9,7 @@ import (
 	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/set"
 	"tailscale.com/util/syspolicy/internal"
+	"tailscale.com/util/testenv"
 )
 
 // TestState represents a metric name and its expected value.
@@ -19,13 +20,13 @@ type TestState struct {
 
 // TestHandler facilitates testing of the code that uses metrics.
 type TestHandler struct {
-	t internal.TB
+	t testenv.TB
 
 	m map[string]int64
 }
 
 // NewTestHandler returns a new TestHandler.
-func NewTestHandler(t internal.TB) *TestHandler {
+func NewTestHandler(t testenv.TB) *TestHandler {
 	return &TestHandler{t, make(map[string]int64)}
 }