[DO NOT MERGE] Email notification system (#4338)

* Migration

* Fixup db models

* Redis

* Stuff

* Switch PKs to BIGSERIALs, insert to notifications_deliveries when inserting notifications

* Queue, templates

* Query cache

* Fixes, fixtures

* Perf, cache template data & HTML bodies

* Notification type configuration, ResetPassword notification type

* Reset password

* Query cache

* Clippy + fmt

* Traces, fix typo, fix user email in ResetPassword

* send_email

* Models, db

* Remove dead code, adjust notification settings in migration

* Clippy fmt

* Delete dead code, fixes

* Fmt

* Update apps/labrinth/src/queue/email.rs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Remove old fixtures

* Unify email retry delay

* Fix type

* External notifications

* Remove `notifications_types_preference_restrictions`, as user notification preferences is out of scope for this PR

* Query cache, fmt, clippy

* Fix join in get_many_user_exposed_on_site

* Remove migration comment

* Query cache

* Update html body urls

* Remove comment

* Add paymentfailed.service variable to PaymentFailed notification variant

* Fix compile error

* Fix deleting notifications

* Update apps/labrinth/src/database/models/user_item.rs

Co-authored-by: Josiah Glosson <soujournme@gmail.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Update apps/labrinth/src/database/models/user_item.rs

Co-authored-by: Josiah Glosson <soujournme@gmail.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Update Cargo.toml

Co-authored-by: Josiah Glosson <soujournme@gmail.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Update apps/labrinth/migrations/20250902133943_notification-extension.sql

Co-authored-by: Josiah Glosson <soujournme@gmail.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Address review comments

* Fix compliation

* Update apps/labrinth/src/database/models/users_notifications_preferences_item.rs

Co-authored-by: Josiah Glosson <soujournme@gmail.com>
Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>

* Use strfmt to format emails

* Configurable Reply-To

* Configurable Reply-To

* Refactor for email background task

* Send some emails inline

* Fix account creation email check

* Revert "Use strfmt to format emails"

This reverts commit e0d6614afe51fa6349918377e953ba294c34ae0b.

* Reintroduce fill_template

* Set password reset email inline

* Process more emails per index

* clippy fmt

* Query cache

---------

Signed-off-by: François-Xavier Talbot <108630700+fetchfern@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Josiah Glosson <soujournme@gmail.com>

apps/labrinth/src/database/models/user_item.rs

@@ -233,7 +233,7 @@ impl DBUser {
         exec: E,
     ) -> Result<Option<DBUserId>, sqlx::Error>
     where
-        E: sqlx::Executor<'a, Database = sqlx::Postgres> + Copy,
+        E: sqlx::Executor<'a, Database = sqlx::Postgres>,
     {
         let user = sqlx::query!(
             "
@@ -254,7 +254,7 @@ impl DBUser {
         exec: E,
     ) -> Result<Vec<DBUserId>, sqlx::Error>
     where
-        E: sqlx::Executor<'a, Database = sqlx::Postgres> + Copy,
+        E: sqlx::Executor<'a, Database = sqlx::Postgres>,
     {
         let users = sqlx::query!(
             "
@@ -270,13 +270,32 @@ impl DBUser {
         Ok(users)
     }
 
+    /// Returns `false` if any of the specified user IDs do not exist.
+    pub async fn exists_many<'a, E>(
+        user_ids: &[DBUserId],
+        exec: E,
+    ) -> Result<bool, sqlx::Error>
+    where
+        E: sqlx::Executor<'a, Database = sqlx::Postgres>,
+    {
+        let ids = user_ids.iter().map(|x| x.0).collect::<Vec<_>>();
+        let count = sqlx::query_scalar!(
+            r#"SELECT COUNT(*) "count!" FROM users WHERE id = ANY($1)"#,
+            &ids
+        )
+        .fetch_one(exec)
+        .await?;
+
+        Ok(count as usize == user_ids.len())
+    }
+
     pub async fn get_projects<'a, E>(
         user_id: DBUserId,
         exec: E,
         redis: &RedisPool,
     ) -> Result<Vec<DBProjectId>, DatabaseError>
     where
-        E: sqlx::Executor<'a, Database = sqlx::Postgres> + Copy,
+        E: sqlx::Executor<'a, Database = sqlx::Postgres>,
     {
         use futures::stream::TryStreamExt;
 
@@ -324,7 +343,7 @@ impl DBUser {
         exec: E,
     ) -> Result<Vec<DBOrganizationId>, sqlx::Error>
     where
-        E: sqlx::Executor<'a, Database = sqlx::Postgres> + Copy,
+        E: sqlx::Executor<'a, Database = sqlx::Postgres>,
     {
         use futures::stream::TryStreamExt;
 
@@ -349,7 +368,7 @@ impl DBUser {
         exec: E,
     ) -> Result<Vec<DBCollectionId>, sqlx::Error>
     where
-        E: sqlx::Executor<'a, Database = sqlx::Postgres> + Copy,
+        E: sqlx::Executor<'a, Database = sqlx::Postgres>,
     {
         use futures::stream::TryStreamExt;
 
@@ -373,7 +392,7 @@ impl DBUser {
         exec: E,
     ) -> Result<Vec<DBProjectId>, sqlx::Error>
     where
-        E: sqlx::Executor<'a, Database = sqlx::Postgres> + Copy,
+        E: sqlx::Executor<'a, Database = sqlx::Postgres>,
     {
         use futures::stream::TryStreamExt;
 
@@ -397,7 +416,7 @@ impl DBUser {
         exec: E,
     ) -> Result<Vec<DBReportId>, sqlx::Error>
     where
-        E: sqlx::Executor<'a, Database = sqlx::Postgres> + Copy,
+        E: sqlx::Executor<'a, Database = sqlx::Postgres>,
     {
         use futures::stream::TryStreamExt;
 
@@ -421,7 +440,7 @@ impl DBUser {
         exec: E,
     ) -> Result<Vec<String>, sqlx::Error>
     where
-        E: sqlx::Executor<'a, Database = sqlx::Postgres> + Copy,
+        E: sqlx::Executor<'a, Database = sqlx::Postgres>,
     {
         use futures::stream::TryStreamExt;