Improve pagination for endpoints tat use SyncCursorPage

[CakeCrusher]

Several endpoints using SyncCursorPage have a implementation for before and after that don't make sense given the current id generation.
Example:

def get_messages(
    db: Session,
    thread_id: str,
    limit: int,
    order: str,
    after: str,
    before: str,
):  # TODO: before and after work in a strange way
    query = db.query(models.Message).filter(
        models.Message.thread_id == thread_id
    )

    if order == "asc":
        query = query.order_by(
            asc(models.Message.created_at), asc(models.Message.id)
        )
    else:
        query = query.order_by(
            desc(models.Message.created_at), desc(models.Message.id)
        )

    if after:
        last_seen_message = (
            db.query(models.Message).filter(models.Message.id == after).first()
        )
        if last_seen_message:
            query = query.filter(
                models.Message.created_at >= last_seen_message.created_at
            )

    if before:
        first_seen_message = (
            db.query(models.Message)
            .filter(models.Message.id == before)
            .first()
        )
        if first_seen_message:
            query = query.filter(
                models.Message.created_at <= first_seen_message.created_at
            )

    return query.limit(limit).all()