Add expect handler and simplify apps

[mosquito]

@meyerj what do you think if the current app is ContextVar now?

[Copilot]

Pull Request Overview

This PR adds an HTTP Expect: 100-continue handler to the ASGI app and refactors the internal apps stack management in ASGIMatchInfo.

• Introduces a new POST /upload endpoint that returns the parsed Expect header and body size.
• Adds a basic integration test for the Expect handler.
• Refactors ASGIMatchInfo to use a ContextVar for the current app and defines a ResourceInfoDict TypedDict.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
tests/test_fastapi_integration.py	Added imports, /upload endpoint, and test_expect_handler_basic
aiohttp_asgi/resource.py	Refactored ASGIMatchInfo to use ContextVar; added ResourceInfoDict

Comments suppressed due to low confidence (1)

tests/test_fastapi_integration.py:179

• The response includes received_expect but the test does not assert its value. Add an assertion like assert data["received_expect"] == "100-continue" to ensure the header is handled correctly.

assert data["body_size"] == len(test_data)