chore(runtime-sdk): relocate asgi.py into workers directory for consistency

[ryanking13]

moving asgi.py to workers/asgi.py so that users can import both wsgi and asgi modules from

from workers import asgi
from workers import wsgi

I made the existing asgi.py work as-is by importing from workers/asgi.py and re-exporting.

[ask-bonk]

I've reviewed the full diff and all changed files. The changes are straightforward:

1. The original asgi.py content moved verbatim to workers/asgi.py.
2. The old asgi.py replaced with a sys.modules shim to maintain backward compatibility.
3. A test verifies the shim makes the legacy and new module the same object.

The sys.modules[__name__] = _asgi trick is a well-known Python idiom for module aliasing -- after execution, any import of asgi gets the workers.asgi module object, so all attributes, functions, and even __getattr__ resolve identically. The test at line 15-18 correctly validates this.

No logic bugs, no security issues, no backward compatibility problems. The test coverage is appropriate.

LGTM

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