Follow-up: use asyncify in ModuleHost::call

[coolreader18]

Description of Changes

Follow-up to #2737. I added this utility function in #2730, and it makes the logic of these kinds of spawn_blocking uses clearer.

Expected complexity level and risk

1

Testing

n/a - the code is equivalent.

[coolreader18]

I also edited the comment - it's obviously not that we care about having to use std::panic::AssertUnwindSafe, it's that the operation is blocking.

[coolreader18]

There's a similar use in HostController::using_database, ftr:

    pub async fn using_database<F, T>(&self, database: Database, replica_id: u64, f: F) -> anyhow::Result<T>
    where
        F: FnOnce(&RelationalDB) -> T + Send + 'static,
        T: Send + 'static,
    {
        trace!("using database {}/{}", database.database_identity, replica_id);
        let module = self.get_or_launch_module_host(database, replica_id).await?;
        let on_panic = self.unregister_fn(replica_id);
        scopeguard::defer_on_unwind!({
            warn!("database operation panicked");
            on_panic();
        });
        let result = asyncify(move || f(&module.replica_ctx().relational_db)).await;
        Ok(result)
    }