LIMIT ignored in subqueries

The following query works fine and returns the most recent record for each group:
```
SELECT something FROM WHERE time >= now() - 1h GROUP BY "tag1", "tag2" ORDER BY time DESC LIMIT 1
```

However, if we want to use it inside a subquery, we do not get the expected result.

```
SELECT * FROM (SELECT something FROM WHERE time >= now() - 1h GROUP BY "tag1", "tag2" ORDER BY time DESC LIMIT 1)
```
fails with:
```
ERR: subqueries must be ordered in the same direction as the query itself
```

and

```
SELECT * FROM (SELECT something FROM WHERE time >= now() - 1h GROUP BY "tag1", "tag2" ORDER BY time DESC LIMIT 1) ORDER BY time DESC
```
does not fail but returns different data (tags turned into fields) and multiple results per group instead of just one, as asked via `LIMIT 1`.

Reproduce both query examples against InfluxDB and compare the nested query's grouping, ordering, tags, and LIMIT behavior with the standalone query. Trace how subqueries apply ORDER BY, GROUP BY, and LIMIT. Done means the subquery preserves one most-recent record per group without requiring matching outer ordering or converting tags into fields.

Written by the indexing model from the issue text.