♻️ Refactor cocurrency model on backend

Mainly the followin changes:

- Pass majority of code to the old and plain synchronous style
  and start using virtual threads for the RPC (and partially some
  HTTP server middlewares).
- Make some improvements on how CLIMIT is handled, simplifying code
- Improve considerably performance reducing the reflection and
  unnecesary funcion calls on the whole stack-trace of an RPC call.
- Improve efficiency reducing considerably the total threads number.

backend/test/backend_tests/rpc_cond_middleware_test.clj

@@ -40,6 +40,6 @@
               {:keys [error result]} (th/command! (assoc params ::cond/key etag))]
           (t/is (nil? error))
           (t/is (fn? result))
-          (t/is (= 304 (-> (result nil) :status))))
+          (t/is (= 304 (-> (result nil) :yetti.response/status))))
         ))))