fix: Drop messages encrypted with the wrong symmetric secret (#7963)

The tests were originally generated with AI and then reworked.

Follow-up to https://github.com/chatmail/core/pull/7754 (c724e29)

This prevents the following attack:

/// Eve is subscribed to a channel and wants to know whether Alice is also subscribed to it.
/// To achieve this, Eve sends a message to Alice
/// encrypted with the symmetric secret of this broadcast channel.
///
/// If Alice sends an answer (or read receipt),
/// then Eve knows that Alice is in the broadcast channel.
///
/// A similar attack would be possible with auth tokens
/// that are also used to symmetrically encrypt messages.
///
/// To prevent this, a message that was unexpectedly
/// encrypted with a symmetric secret must be dropped.

src/sql.rs

@@ -302,7 +302,7 @@ impl Sql {
     /// otherwise allocates write connection.
     ///
     /// Returns the result of the function.
-    async fn call<'a, F, R>(&'a self, query_only: bool, function: F) -> Result<R>
+    pub async fn call<'a, F, R>(&'a self, query_only: bool, function: F) -> Result<R>
     where
         F: 'a + FnOnce(&mut Connection) -> Result<R> + Send,
         R: Send + 'static,