The hyperfile build is selected by feature. `blocking` stays the default; `reactor`
matches hyperfile's own default build, so the cleaner can share a binary with a
crate that uses hyperfile with its default features:

    hyperfile-cleaner = { version = "0.10", default-features = false, features = ["reactor"] }

compact now finishes on a file whose data is far apart. It used to ask about every
index from 0 to EOF, which for blocks at 1 << 56 never ended; it now asks only
about the windows the bmap walk found mapped blocks in.

collect, prune and report are Send in both builds; compact is not, in either.

Requires hyperfile 0.10.3.