🐛 Recognize custom FastAPI/APIRouter naming patterns (aliases, subclasses, module imports)

[savannahostrowski]

Closes #102, #105, #106

This PR refactors a solid chunk of the router extractor to handle custom naming. For example:

from fastapi import FastAPI as FA 
app = FA()

from fastapi import APIRouter as AR 
router = AR()

import fastapi as f 
app = f.FastAPI()

# Custom subclass
class MyRouter(APIRouter)
router = MyRouter()

# Aliased base class
class MyRouter(AR)

# FastAPI subclass 
class MyApp(FastAPI) 
app = MyApp()

Also fixes CodeLens links in test files when the URL is passed as a keyword argument (client.get(url="/path")).