feature wish(imap-types): iterator on simplified+cleanup ranges in a SequenceSet

[Armael]

Currently, SequenceSet::iter() allows iterating on the individual indexes that the SequenceSet represents.
I would like to be able to iterate on the ranges represented by the SequenceSet before they get expanded into indices, but after they are simplified and cleaned up.
The motivation is to be able to perform efficient range queries when the underlying storage supports it.

If this sounds reasonable I can try to volunteer an implementation.

[duesee]

Hey @Armael! I am not sure how simplification+keeping ranges will look like, but I am open to the idea :-)

What I had in mind at some point was to do something like: First simplify. Then "chunk" so that we can iterate in blocks of 50 sequence numbers or so.