I just as little beyond the type as possible, so the implementation
changes this enables can be reviewed separately.

The downsides is that the coroutine has byte-by-byte loop transfer. Will
fix that next.

Rather than copying byte-by-byte, we let the coroutine know how much
data we would like it to send back to us.

This reverts commit a2c2702. See
addToStoreSlow(), we don't need to handle this case efficiently
anymore. In fact, we can almost remove the method/hashAlgo arguments
since the non-recursive and/or non-SHA256 are almost not used anymore.

This was completely broken since d897231.

…from-dump-stream

This reverts commit cff2157.

I got it to just become `LocalStore::addToStoreFromDump`, cleanly taking
a store and then doing nothing too fancy with it.

`LocalStore::addToStore(...Path...)` is now just a simple wrapper with a
bare-bones sinkToSource of the right dump command.

This reverts commit 592851f. We don't
need this extra feature anymore

We use this to simplify `LocalStore::addToStoreFromDump`.

Also, hope I fixed build error with old clang (used in Darwin CI).

…o git-objects-develop