Split native extension into a second gem

[eliias]

Problem

Building the binaries for the native extensions takes a relatively long time (~40 min), and we actually do not have to do this regularly. Other projects have extracted large binaries into a second gem, to make the process of developing the actual feature set faster.

Tasks

• Convert this repo into a monorepo of two gems, one for isorun and one for isorun-binary.