Refactor EvalState to not use Arcs, label Store's significant drops#59

Naxdy wants to merge 3 commits into

nixops4:mainnixops4/nix-bindings-rust:mainfrom

DeterminateSystems:upstream-feat/eval-state-inner-arcDeterminateSystems/nix-bindings-rust:upstream-feat/eval-state-inner-arcCopy head branch name to clipboard