internal/pkg: cache flags

This is cleaner for extending the API.

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

internal/pkg/file_test.go

@@ -11,9 +11,7 @@ func TestFile(t *testing.T) {
 	t.Parallel()
 
 	checkWithCache(t, []cacheTestCase{
-		{"file", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
-			c.SetStrict(true)
-
+		{"file", pkg.CValidateKnown, nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
 			cureMany(t, c, []cureStep{
 				{"short", pkg.NewFile("null", []byte{0}), base.Append(
 					"identifier",