v1: make profile available in summary section?

[wkalt]

This would prevent the need to read from the front of the file when doing indexed reads, which would reduce latency for remote reading by some amount (should be tested).

This doesn't have to break backward compatibility, but would require either a new record type, or else overloading the Header. Strictly speaking, we only need the profile, not the library, but perhaps the library would be useful too.