Tests for IMAP search extensions

Why?

While documenting implemented RFCs for the distributed server, I realized we do not test the two following RFCs:

• https://datatracker.ietf.org/doc/html/rfc5182 Referencing the result of previous IMAP searches.

• https://datatracker.ietf.org/doc/html/rfc4731 Aggregations for IMAP search (min, max, count)

What?

Write basic MPT tests for the following RFCs, because what is untested should not be advertised as supported.

Defects found

While testing this I found a defect in IMAP CONDSTORE for the search commands that ignores only the first range for finding the highest modseq (with one range this is thus fully ignored) due to a bad stop condition in a for loop.