feat(hogql): mixed PoE mode

[mariusandra]

Problem

I've been told we can speed up queries that rely on ingestion-time person properties without the full PoE rollout, by just exposing person_properties.

Changes

Introduces a v1_mixed PoE mode, where properties are taken from the event, but the other fields come via joins.

This only works on HogQL queries.

query = "SELECT event, person.id, person.properties, person.created_at FROM events"

test_cases = [
    (
        PersonsOnEventsMode.disabled, # all joined
        "events.event",
        "events__pdi__person.id",
        "events__pdi__person.properties",
        "toTimeZone(events__pdi__person.created_at, %(hogql_val_0)s)",
    ),
    (
        PersonsOnEventsMode.v1_enabled, # all direct
        "events.event",
        "events.person_id",
        "events.person_properties",
        "toTimeZone(events.person_created_at, %(hogql_val_0)s)",
    ),
    (
        PersonsOnEventsMode.v1_mixed,  # properties direct
        "events.event",
        "events__pdi.person_id",
        "events.person_properties",
        "toTimeZone(events__pdi__person.created_at, %(hogql_val_0)s)",
    ),
]

How did you test this code?

Added tests to document the new behaviour. It's disabled by default, but we could play with it under /debug and try if it makes a difference for real clients.