collab: Return current usage by model from GET /billing/usage (#29693)

This PR updates the `GET /billing/usage` endpoint to return the number
of requests made to each model and mode.

Release Notes:

- N/A

crates/collab/src/llm/db/queries/subscription_usage_meters.rs

@@ -1,3 +1,4 @@
+use crate::db::UserId;
 use crate::llm::db::queries::subscription_usages::convert_chrono_to_time;
 
 use super::*;
@@ -34,4 +35,38 @@ impl LlmDatabase {
         })
         .await
     }
+
+    /// Returns all current subscription usage meters for the given user as of the given timestamp.
+    pub async fn get_current_subscription_usage_meters_for_user(
+        &self,
+        user_id: UserId,
+        now: DateTimeUtc,
+    ) -> Result<Vec<(subscription_usage_meter::Model, subscription_usage::Model)>> {
+        let now = convert_chrono_to_time(now)?;
+
+        self.transaction(|tx| async move {
+            let result = subscription_usage_meter::Entity::find()
+                .inner_join(subscription_usage::Entity)
+                .filter(subscription_usage::Column::UserId.eq(user_id))
+                .filter(
+                    subscription_usage::Column::PeriodStartAt
+                        .lte(now)
+                        .and(subscription_usage::Column::PeriodEndAt.gte(now)),
+                )
+                .select_also(subscription_usage::Entity)
+                .all(&*tx)
+                .await?;
+
+            let result = result
+                .into_iter()
+                .filter_map(|(meter, usage)| {
+                    let usage = usage?;
+                    Some((meter, usage))
+                })
+                .collect();
+
+            Ok(result)
+        })
+        .await
+    }
 }