libbitcoin: 3.4.0 -> 3.5.0

Semi-automatic update generated by https://github.com/ryantm/nix-update tools. These checks were done:

- built on NixOS
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 3.5.0 with grep in /nix/store/ciln99fn6lhwnb1z1h6cyrk6vc4a0ngn-libbitcoin-3.5.0
- directory tree listing: https://gist.github.com/57d42e66f139b59578e1c681316c0ec6