setValue test and benchmark updates

[seebs]

This provides a simple benchmark that can be used for
setValue, to give a way to compare results from adding BSI
support to roaring. Use the BSIGroup prefix for the
fragments, and specify a cache type of "none", to prevent
the use of a LRU cache (which makes things more expensive).

Add a parallel benchmark for ImportValue, so we can compare
them. (Unsurprisingly, the bulk-import endpoint is quite a
lot faster.)

Also, add a test for clearing values to the TestFragment_Sum
test; it turns out that this was never tested in this code,
but the http client test would test it and verify it, it should
probably also be tested here.

Overview

A couple of holes in testing, and some benchmarking I wanted to have around when playing with the performance of SetValue.

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