refactor: don't init config at class definition to allow custom config classes/argparser

[gastmaier]

Description

This PR fixes #1246

Summary

Python's default arguments are evaluated once when the function is defined. Config was instantiated at BaseRobyn class definition and init.py body. Call Config() only inside BaseRobyn, and if not None. At SubRouter, forward the config parameter.

For config.compile_rust_path, access from the class object, and unset to ensure compile_rust_path is called once per config object. Allows to write custom argument parsers without colliding with Config.parser.

This allows to pass implement alternative configs, for example:

from robyn import Robyn, Response as RobynResponse
from robyn.argument_parser import Config as RobynConfig

from .handler import my_route

class AltConfig(RobynConfig):
    def __init__(self) -> None:
        self.disable_openapi = True
        self.dev = False
        self.log_level = "DEBUG"
        self.open_browser = False
        self.fast = 1
        self.workers = 1
        self.processes = 1
        self.compile_rust_path = None

config=AltConfig()
app = Robyn(__file__, config=config)

@app.post("/my-route")
async def route_my_route(request):
    response =  my_route(app.env,  request)
    return RobynResponse(
        status_code=response.status_code,
        headers=response.headers,
        description=response.body,
    )

def main():
    app.start(port=app.env.port)

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High-level PR Summary

This PR refactors how the Config class is initialized in Robyn to fix a bug (#1246) related to Python's default argument evaluation behavior. Instead of initializing the config at class definition and in __init__.py, it now initializes the config inside the BaseRobyn class only when needed. This change enables users to implement custom config classes and argument parsers without colliding with the default Config.parser. The PR also ensures that compile_rust_path is called only once per config object by unsetting it after use.

⏱️ Estimated Review Time: 5-15 minutes

💡 Review Order Suggestion

Order	File Path
1	robyn/__init__.py

[recurseml]

Review by RecurseML

🔍 Review performed on 118660f..448338b

✨ No bugs found, your code is sparkling clean

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Project	Deployment	Preview	Comments	Updated (UTC)
robyn	Error			Sep 23, 2025 7:48pm

[recurseml]

Review by RecurseML

🔍 Review performed on 448338b..448338b

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[sansyrox]

@gastmaier , thanks for the PR. I have been on a break for a while. Will review this PR soon. :D

[sansyrox]

@gastmaier , have you tested this in --dev mode?

[gastmaier]

There shouldn't be any issues with dev mode, just resolved the multiple instantiation of Config() due to the behaviour of the Python interpreter.