[py] Add expect_* context managers for BiDi events

[AutomatedTester]

Summary

Adds high-level expect_* context managers for BiDi events to the Python bindings, giving users a race-free way to wait for an event triggered by an action.

A new Subscription primitive registers its event handler at creation time — so an event fired by an action inside the with block cannot be missed:

with driver.network.expect_response("**/api/**") as response_info:
    driver.find_element(By.ID, "load").click()
response = response_info.value

New high-level methods (generated via the enhancements manifest)

• network.expect_request / network.expect_response — URL glob or predicate filtering, with observational Request/Response wrappers
• script.expect_console_message — predicate over ConsoleMessage
• browsing_context.expect_user_prompt — typed prompt params
• browsing_context.expect_download — correlates downloadWillBegin and downloadEnd by navigation id into a new Download object with path(), save_as() and failure()

The event manager gains a raw=True option so expect_* handlers receive the full wire-level params instead of the generated dataclasses, which drop fields like request/response.

Testing

• 25 unit tests
• 6 browser-based integration tests

Cross-binding impact

This is a Python-only ergonomic layer over existing BiDi primitives; no wire-level behavior changes. Parity work for other bindings (Java/Ruby/JS/.NET) is a possible follow-up.