ident: isolate non-system component of member

This enables more efficient representation in contexts inherently namespaced to the current system.

Signed-off-by: Yonah <contrib@gensokyo.uk>

ident/ident_test.go

@@ -117,15 +117,17 @@ func TestFM(t *testing.T) {
 
 		{"valid", ident.F[ident.M, *ident.M]{
 			I: &ident.M{
-				Serial: 0xfdfdfdfdfdfdfdfd,
+				PartM: ident.PartM{
+					Serial: 0xfdfdfdfdfdfdfdfd,
 
-				Time: uint64(time.Date(
-					0xfd, 7, 15,
-					23, 59, 59, 0xcab,
-					time.UTC,
-				).UnixNano()),
+					Time: uint64(time.Date(
+						0xfd, 7, 15,
+						23, 59, 59, 0xcab,
+						time.UTC,
+					).UnixNano()),
 
-				ID: 0x2e736e64,
+					ID: 0x2e736e64,
+				},
 
 				System: ident.S{
 					Site: ident.TrivialSite,