Nix update procedure

1. bump version in Cargo.toml and nix/package.nix
2. in nix/package.nix replace src and cargoHash as follows:

  src = lib.cleanSource ../.;
  cargoHash = lib.fakeHash;

3. run cd nix && ./build.sh and replace cargoHash from command output with got: sha256-THISISTHEHASHYOUSHOULDREPLACEITWITH=
4. undo the change to src = lib.cleanSource back to src = fetchFromGithub
5. run nix --extra-experimental-features nix-command store prefetch-file --unpack --json https://github.com/REPLACE_WITH_PR_CREATOR/iroh-ssh/archive/REPLACE_WITH_COMMIT_HASH.tar.gz | jq -r '.hash'
6. replace src fetchFromGithub hash with output from step 5.

note: for testing you might have to replace tag with rev and put the github commit id in there