[IMPL] - Custom backend server and improved configuration capabilities

[KronosDev-Pro]

Original PR: #4337

Idea

Customize the backend server configuration as you like, and create a complete new backend server support.

can be easily split into another reflex package, for example pip install reflex[granian].

Example

We can define which BackendServer to use for development and production modes and thus customize the configuration (all parameters for each BackendServer are the actual parameters corresponding to the web server involved).

import reflex as rx
from reflex import server

config = rx.Config(
    app_name="examples",
    backend_server_dev = server.GunicornBackendServer(
        worker_class="uvicorn.workers.UvicornH11Worker",
        max_requests=100,
        max_requests_jitter=25,
        timeout=120,
        threads=1,
        workers=1,
    ),
    backend_server_prod = server.GranianBackendServer(
        threads=2,
        workers=4,
    )
)

We can also create a customized BackendServer with the CustomBackendServer class, such as GranianBackendServer

---

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• New feature (non-breaking change which adds functionality)
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[KronosDev-Pro]

@adhami3310 this is the new PR, apparently it solved the problems

I will test again, with a different version of python and other sample projects. ✔️