test: move application tests to tests/

test_support/test_helpers -> tests/support; watched_at unified w/ domain test_watched_at (2024-03-15).
Kept inline: users::diary_filter tests (feed_sort_to_direction_all_variants, paged_user_filter_builds_correctly) - pub(super) helpers in private module.
Dropped stale never-compiled users/tests/get_users.rs (old execute signature).

crates/application/src/movies/request_enrichment.rs

@@ -42,7 +42,3 @@ pub async fn fetch_if_stale(
         Err(e) => Err(e),
     }
 }
-
-#[cfg(test)]
-#[path = "tests/request_enrichment.rs"]
-mod tests;