Fix top level randomness in aiohttp

[hoodmane]

aiohttp instantiates a random.Random() in order to be a default argument for WebSocketWriter. Instead, use the random module itself for this which implements the same interface as Random.

Should fix one of the test failures in #2096.

[hoodmane]

It works:

2024-05-09T20:58:32.9101316Z //src/workerd/server/tests/python:import/aiohttp/import    
PASSED in 26.5s

[garrettgu10]

Merged as part of #2096 🥳