Generalize `Page.on` beyond `"console"` events (#2875)

# why

Generalize the system and types to handle more than `"console"` events
for `Page.on` listeners.

# what changed

- `PageCDPEvent` schema now has `method: z.enum` parameter.
- We propagate through the page event (today, still just `"console"`)
down to the CDP subscription manager.

# test plan

This refactor introduces no functional changes. We update existing tests
to in preparation for more events. All tests should continue passing.