♻️ Add minor refactor for internal concurrency model

Replace general usage of virtual threads with platform threads
and use virtual threads for lightweight procs such that websocket
connections. This decision is made mainly because virtual threads
does not appear on thread dumps in an easy way so debugging issues
becomes very difficult.

The threads requirement of penpot for serving http requests
is not very big so having so this decision does not really affects
the resource usage.

backend/test/backend_tests/helpers.clj

@@ -113,7 +113,6 @@
                              :app.auth.oidc.providers/generic
                              :app.setup/templates
                              :app.auth.oidc/routes
-                             :app.worker/monitor
                              :app.http.oauth/handler
                              :app.notifications/handler
                              :app.loggers.mattermost/reporter