core: optimize group deletion (delays deletion of unused contacts) (#2560)

* core: optimize group deletion (wip)

* delay deletion of unused contacts

* clean up, fix test

* rename field

* remove from type, more checks, remove ctx

* remove space

* rename functions

* rename

---------

Co-authored-by: Evgeny Poberezkin <2769109+epoberezkin@users.noreply.github.com>

src/Simplex/Chat/Controller.hs

@@ -112,6 +112,7 @@ data ChatConfig = ChatConfig
     testView :: Bool,
     initialCleanupManagerDelay :: Int64,
     cleanupManagerInterval :: NominalDiffTime,
+    cleanupManagerStepDelay :: Int64,
     ciExpirationInterval :: Int64 -- microseconds
   }