refactor: Make ConnectivityStore use a non-async lock (#7129)

Follow-up to https://github.com/chatmail/core/pull/7125: We now have a
mix of non-async (parking_lot) and async (tokio) Mutexes used for the
connectivity. We can just use non-async Mutexes, because we don't
attempt to hold them over an await point. I also tested that we get a
compiler error if we do try to hold one over an await point (rather than
just deadlocking/blocking the executor on runtime).

Not 100% sure about using the parking_lot rather than std Mutex, because
since https://github.com/rust-lang/rust/issues/93740, parking_lot
doesn't have a lot of advantages anymore. But as long as iroh depends on
it, we might as well use it ourselves.

deltachat-jsonrpc/src/api.rs

@@ -1908,7 +1908,7 @@ impl CommandApi {
     /// If the connectivity changes, a #DC_EVENT_CONNECTIVITY_CHANGED will be emitted.
     async fn get_connectivity(&self, account_id: u32) -> Result<u32> {
         let ctx = self.get_context(account_id).await?;
-        Ok(ctx.get_connectivity().await as u32)
+        Ok(ctx.get_connectivity() as u32)
     }
 
     /// Get an overview of the current connectivity, and possibly more statistics.