metric_hyperplane_partitioner is not compatible with key-value containers

[bwpriest]

Currently in v0.3-dev, if you pass a key-value store to saltatlas::dhnsw::partition_data(), such as a ygm::container::map, the for_all()s in saltatlas::metric_hyperplane_partitioner barf because they expect a bag of pairs. The offending lines occur here, here, here, and here.

It should be possible to specify compile-time constexpr conditionals so that the correct signature is used depending on the for_all arguments of the container, although I am not sure if YGM v0.7-dev has a more elegant solution to this.

This issue is currently a blocker on updating hdknn to use v0.3-dev and the simple API.