nix flake

[vnprc]

Migrate to a nix flake build that makes it easy to lock dependencies to a known stable version.

I've started this work with flake.nix but it's still broken. I am unable to start the devenv environment from within the nix shell.

Steps to reproduce:

• check out the nixfix branch
• nix develop
• devenv up

[vnprc]

I removed the nix flake entirely in favor of a devenv build with hard coded bitcoind commit hash.

#31 (comment)