Move Regional Records computation to Auxiliary table

[gregorbg]

Supersedes #10089, although I'm very grateful for the initial inspiration 😄
Supersedes #10120

The basic problem is that the query to pre-load existing records was breaking our necks. The simple solution of this PR is to combine Results data and Competitions data into one common, JOINed table which can be indexed.
That way, we can essentially reuse the same queries as before (with minor modifications to the table name etc.) but the indexes will make them reasonably fast.

Before

SELECT r.eventId, r.countryId, MIN(r.best) AS `value`
FROM (
  SELECT `Results`.`eventId`, `Results`.`competitionId`, `Results`.`countryId`, `Results`.`best`
  FROM `Results`
  WHERE `Results`.`best` > 0
) AS r
INNER JOIN (
  SELECT `Competitions`.`id`
  FROM `Competitions`
  WHERE `Competitions`.`end_date` < '2024-08-10' # This seemingly hard-coded value is read directly from the `Competitions` table one step before
) AS c
  ON c.id = r.competitionId
INNER JOIN (
  SELECT `competition_events`.`event_id`
  FROM `competition_events`
  WHERE `competition_events`.`competition_id` = 'StevenageAugust2024'
) AS ce
  ON ce.event_id = r.eventId
GROUP BY r.eventId, r.countryId

Benchmark on my local machine: 11390.9ms

After

⚠️ Please do not be confused by the table being referenced as Results. This is a necessary hack because otherwise the Rails model engine gets confused! It is only an alias that is freely choosable, and in terms of understanding the contents of this query, you can mentally replace Results with pancake.

SELECT eventId, countryId, MIN(best) AS `value`
FROM regional_records_lookup AS Results # This alias is here only to make sure that Ruby doesn't get confused
WHERE `Results`.`best` > 0
  AND `Results`.`competitionEndDate` < '2024-08-10'
  AND `Results`.`eventId` IN ('333', '222', '444', '555', '666', '777', '333bf', '333fm', '333oh', 'clock', 'minx', 'pyram', 'sq1')
GROUP BY `Results`.`eventId`, `Results`.`countryId`

The relevant index is on (eventId, countryId, competitionEndDate, best) (as well as (eventId, countryId, competitionEndDate, average) respectively for averages)

Benchmark on my local machine: 1804.1ms

[danieljames-dj]

Maybe replace "after the results posting" with "after the 'import results' step", so that it won't get confused with last step?