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/allocs.go

@@ -6,8 +6,9 @@ package tstest
 import (
 	"fmt"
 	"runtime"
-	"testing"
 	"time"
+
+	"tailscale.com/util/testenv"
 )
 
 // MinAllocsPerRun asserts that f can run with no more than target allocations.
@@ -16,7 +17,7 @@ import (
 //
 // MinAllocsPerRun sets GOMAXPROCS to 1 during its measurement and restores
 // it before returning.
-func MinAllocsPerRun(t *testing.T, target uint64, f func()) error {
+func MinAllocsPerRun(t testenv.TB, target uint64, f func()) error {
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
 
 	var memstats runtime.MemStats