Add custom typing to config and ctx

[ahopkins]

One thing I have always found slightly annoying is that the reliance upon app.ctx and app.config lead to only partially typed objects. This PR attempts to resolve that by adding some generics into sanic.Sanic and sanic.Request:

app: Sanic[CustomConfig, CustomCtx]

This can also be achieved by implication just through instantiation:

from sanic import Sanic
app = Sanic("test")
reveal_type(app)  # N: Revealed type is "sanic.app.Sanic[sanic.config.Config, types.SimpleNamespace]"

from sanic import Sanic
from sanic.config import Config

class CustomConfig(Config):
    pass

app = Sanic("test", config=CustomConfig())
reveal_type(app)  # N: Revealed type is "sanic.app.Sanic[main.CustomConfig, types.SimpleNamespace]"

from sanic import Sanic

class Foo:
    pass

app = Sanic("test", ctx=Foo())
reveal_type(app)  # N: Revealed type is "sanic.app.Sanic[sanic.config.Config, main.Foo]"

from sanic import Sanic
from sanic.config import Config

class CustomConfig(Config):
    pass

class Foo:
    pass

app = Sanic("test", config=CustomConfig(), ctx=Foo())
reveal_type(app)  # N: Revealed type is "sanic.app.Sanic[main.CustomConfig, main.Foo]"

The goal of this PR is a nicer dev experience to be able to fully type out the ctx and config objects.

Given a simple handler with no custom typing:

@app.get("/")
async def handler(request: Request):
    reveal_type(request.app)

Or, a fully custom typed:

A side benefit is that sanic.Request.ctx is now a lazy object and will not be instantiated until used. This is accomplished by introducing a new staticmethod on the Request object. It can be used to instantiate a custom ctx object as shown in the above screenshot. This is the only functional change in this PR: moving self.ctx = SimpleNamespace() into the lazy make_context pattern.

TODO:

• Add generics also to Request.ctx
• Add generics also to Request so that it can pass the ref in a handler for example

[codecov]

Codecov Report

Patch coverage: 89.473% and project coverage change: -0.081 ⚠️

Comparison is base (929d270) 88.887% compared to head (044675d) 88.806%.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #2785       +/-   ##
=============================================
- Coverage   88.887%   88.806%   -0.081%     
=============================================
  Files           92        92               
  Lines         7001      7031       +30     
  Branches      1194      1195        +1     
=============================================
+ Hits          6223      6244       +21     
- Misses         531       538        +7     
- Partials       247       249        +2     

Impacted Files	Coverage Δ
sanic/blueprints.py	91.743% <ø> (ø)
sanic/errorpages.py	98.780% <ø> (ø)
sanic/headers.py	96.059% <ø> (ø)
sanic/router.py	96.000% <ø> (ø)
sanic/server/websockets/frame.py	92.523% <ø> (ø)
sanic/app.py	89.072% <76.470%> (-1.097%)	⬇️
sanic/__init__.py	100.000% <100.000%> (ø)
sanic/exceptions.py	97.247% <100.000%> (ø)
sanic/request/types.py	94.915% <100.000%> (+0.163%)	⬆️
sanic/server/websockets/impl.py	37.674% <100.000%> (+0.232%)	⬆️

... and 1 file with indirect coverage changes

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