Fix random_projects route not returning the requested number of projects (#3758)

* Fix random_projects route not returning the requested number of projects

* fix(labrinth): further improve random project route SQL query

* chore: fix typo in comment

* tweak(labrinth): more apparent and fast randomness for `random_projects_get`

* tweak(labrinth): even better random projects query

* chore: address formatting review

---------

Co-authored-by: Alejandro González <me@alegon.dev>

apps/labrinth/src/routes/v3/projects.rs

@@ -94,14 +94,17 @@ pub async fn random_projects_get(
     })?;
 
     let project_ids = sqlx::query!(
-        "
-            SELECT id FROM mods TABLESAMPLE SYSTEM_ROWS($1) WHERE status = ANY($2)
-            ",
-        count.count as i32,
+        // IDs are randomly generated (see the `generate_ids` macro), so ID order is
+        // equivalent to a random order
+        "SELECT id FROM mods WHERE status = ANY($1)
+        ORDER BY id
+        LIMIT $2
+        OFFSET GREATEST(ROUND(RANDOM() * (SELECT COUNT(*) FROM mods WHERE status = ANY($1)))::int8 - $2, 0)",
         &*crate::models::projects::ProjectStatus::iterator()
             .filter(|x| x.is_searchable())
             .map(|x| x.to_string())
             .collect::<Vec<String>>(),
+        count.count as i32,
     )
     .fetch(&**pool)
     .map_ok(|m| db_ids::DBProjectId(m.id))