tstest, util/testenv: drop tstest's dependency on the testing package

Change tstest's exported functions (AssertNotParallel, Replace,
Parallel, RequireRoot, SkipOnKernelVersions, MinAllocsPerRun, FixLogs,
UnfixLogs, CheckIsZero, ResourceCheck) to take testenv.TB instead of
testing.TB or *testing.T, so importing tstest from non-test code no
longer links the testing package and its flag registration side
effects into the binary. Add testenv.Verbose to replace the one use of
testing.Verbose, and a deptest check to keep testing out of tstest's
dependency graph.

Callers are unaffected: *testing.T and testing.TB both satisfy
testenv.TB.

Updates tailscale/corp#45223

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: Ib373ff66ceff638d071582baf8367245987e9155

tstest/resource.go

@@ -9,8 +9,9 @@ import (
 	"runtime/pprof"
 	"slices"
 	"strings"
-	"testing"
 	"time"
+
+	"tailscale.com/util/testenv"
 )
 
 // ResourceCheck takes a snapshot of the current goroutines and registers a
@@ -19,7 +20,7 @@ import (
 // can look at specific routines).
 //
 // It panics if called from a parallel test.
-func ResourceCheck(tb testing.TB) {
+func ResourceCheck(tb testenv.TB) {
 	tb.Helper()
 
 	// Set an environment variable (anything at all) just for the
@@ -48,7 +49,7 @@ func ResourceCheck(tb testing.TB) {
 		// Parse and print goroutines.
 		start := parseGoroutines(startStacks)
 		end := parseGoroutines(endStacks)
-		if testing.Verbose() {
+		if testenv.Verbose() {
 			tb.Logf("goroutines start:\n%s", printGoroutines(start))
 			tb.Logf("goroutines end:\n%s", printGoroutines(end))
 		}