Use a read-only store

[layus]

This is an example of how we could make hnix use a read-only store because it makes little sense to use the remote daemon in the current state of the project.

1. Using the daemon makes tests complex
2. We cannot do anything useful with the daemon atm (except generating raw files and .drv in the store)
3. The daemon is not used as intended, as we do not persist the connection across calls.

See haskell-nix/hnix-store#144

[sorki]

Good idea! Daemon tests can wait until I manage to decouple -remote test framework and make it usable by hnix as well.

[layus]

Got stale, but the rebase is fairly trivial. Still waiting on a release of hnix-store-core >= 0.4.3 in nixpkgs in order to get this merged.