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/reflect.go

@@ -6,8 +6,9 @@ package tstest
 import (
 	"net/netip"
 	"reflect"
-	"testing"
 	"time"
+
+	"tailscale.com/util/testenv"
 )
 
 // IsZeroable is the interface for things with an IsZero method.
@@ -30,7 +31,7 @@ var (
 // The nonzeroValues map should contain non-zero values for each type that
 // exists in the type T or any contained types. Basic types like string, bool,
 // and numeric types are handled automatically.
-func CheckIsZero[T IsZeroable](t testing.TB, nonzeroValues map[reflect.Type]any) {
+func CheckIsZero[T IsZeroable](t testenv.TB, nonzeroValues map[reflect.Type]any) {
 	t.Helper()
 
 	var zero T