fix: handle ASGI WebSocket close events and environment propagation

[dom96]

This fixes two gaps in ASGI WebSocket handling:

• Application-originated websocket.close messages were ignored, so clients never received the requested close code or reason.
• WebSocket scopes always received an empty env, even when the caller supplied Worker bindings.

Test Plan

$ uv run pytest 'tests/test_in_workerd.py::test_in_workerd[asgi-ws-disconnect-3.13]' -v

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ProviderModelNotFoundError

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