Allow cosockets, light threads, semaphores and etc in the context of init_by_lua*

It is desired to enable those Lua APIs that might yield in the context of init_by_lua*. It's particularly useful to have the ability to initiate multiple concurrent light threads to (pre)load crucial metadata from some remote services upon startup.

Under the hood, we can simply plant an event loop in the init_by_lua* handler with a configurable timeout protection (to avoid the server from taking too long to start).

Start at the init_by_lua* handler and trace how startup code currently runs; inspect the module's handling of yielding Lua APIs before deciding how they can operate there. Completion should allow the named APIs and concurrent light threads during initialization while enforcing a configurable startup timeout, with coverage for successful loading and timeout behavior.