test: move domain tests to tests/

Self dev-dep w/ test-helpers for domain::testing. Also moved social blanket-impl + InMemoryStore tests (public API only). No private-item exceptions.

crates/domain/tests/models.rs

@@ -0,0 +1,12 @@
+#[path = "models/constructors_test.rs"]
+mod constructors_test;
+#[path = "models/goal_test.rs"]
+mod goal_test;
+#[path = "models/person_test.rs"]
+mod person_test;
+#[path = "models/review_test.rs"]
+mod review_test;
+#[path = "models/stats_test.rs"]
+mod stats_test;
+#[path = "models/watch_event_test.rs"]
+mod watch_event_test;