system: unexport Op implementations

None of these are valid with their zero value, and the implementations assume they are created by the builder methods. They are by all means an implementation detail and exporting them makes no sense.

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

system/mkdir_test.go

@@ -21,7 +21,7 @@ func TestEnsure(t *testing.T) {
 		t.Run(tc.name+"_"+tc.perm.String(), func(t *testing.T) {
 			sys := New(t.Context(), 150)
 			sys.Ensure(tc.name, tc.perm)
-			(&tcOp{User, tc.name}).test(t, sys.ops, []Op{&MkdirOp{User, tc.name, tc.perm, false}}, "Ensure")
+			(&tcOp{User, tc.name}).test(t, sys.ops, []Op{&mkdirOp{User, tc.name, tc.perm, false}}, "Ensure")
 		})
 	}
 }
@@ -38,7 +38,7 @@ func TestEphemeral(t *testing.T) {
 		t.Run(tc.path+"_"+tc.perm.String()+"_"+TypeString(tc.et), func(t *testing.T) {
 			sys := New(t.Context(), 150)
 			sys.Ephemeral(tc.et, tc.path, tc.perm)
-			tc.test(t, sys.ops, []Op{&MkdirOp{tc.et, tc.path, tc.perm, true}}, "Ephemeral")
+			tc.test(t, sys.ops, []Op{&mkdirOp{tc.et, tc.path, tc.perm, true}}, "Ephemeral")
 		})
 	}
 }
@@ -60,7 +60,7 @@ func TestMkdirString(t *testing.T) {
 	}
 	for _, tc := range testCases {
 		t.Run(tc.want, func(t *testing.T) {
-			m := &MkdirOp{
+			m := &mkdirOp{
 				et:        tc.et,
 				path:      container.Nonexistent,
 				perm:      0701,