internal/stub: move from container

This package solves a very specific stubbing use case, in a less than elegant manner.

Signed-off-by: Ophestra <cat@gensokyo.uk>

container/stub/exit.go

@@ -1,44 +0,0 @@
-package stub
-
-import "testing"
-
-// PanicExit is a magic panic value treated as a simulated exit.
-const PanicExit = 0xdead
-
-const (
-	panicFailNow = 0xcafe0 + iota
-	panicFatal
-	panicFatalf
-)
-
-// HandleExit must be deferred before calling with the stub.
-func HandleExit(t testing.TB) {
-	switch r := recover(); r {
-	case PanicExit:
-		break
-
-	case panicFailNow:
-		t.FailNow()
-
-	case panicFatal, panicFatalf, nil:
-		break
-
-	default:
-		panic(r)
-	}
-}
-
-// handleExitNew handles exits from goroutines created by [Stub.New].
-func handleExitNew(t testing.TB) {
-	switch r := recover(); r {
-	case PanicExit, panicFatal, panicFatalf, nil:
-		break
-
-	case panicFailNow:
-		t.Fail()
-		break
-
-	default:
-		panic(r)
-	}
-}