Begin tuning db-get-builds for performancedb-get-builds-performance-tuning

Now that I actually have some experience using SQLite from writing the Guix
Build Coordinator, I can actually see potential ways to improve bits of
Cuirass.

The intention here is to start to address the performance of db-get-builds,
which I think can be quite slow.

This commit does several things, the big change is to try and construct a
simpler query for SQLite. I'm not confident that SQLite's query planner can
look past handling the NULL parameters, so I think it could be helpful to try
and create a simpler query, both to avoid that problem if it exists, but also
move the complexity in to Guile code, which I think is a bit more manageable.

The way ordering is handled is also changed. Order is one of the filters,
although it's not a filter, and some of the other filters also influenced the
order. I think there are things still to fix/improve with the handling of
ordering, but at least this commit just has the ordering happen once in the
query.

If this direction sounds OK, I think the next things to do is do a bit more
testing, both to check uses of this query still work as intended, but also to
take those specific queries generated by db-get-builds, and check what SQLite
says when running them with EXPLAIN QUERY PLAN, as that should inform further
improvements, and what indexes to create.

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