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/src/value_objects/mod.rs

@@ -11,7 +11,3 @@ pub use movie::*;
 pub use review::*;
 pub use social::*;
 pub use user::*;
-
-#[cfg(test)]
-#[path = "../tests/value_objects.rs"]
-mod tests;