ddar: move out of pythonPackages and fix tests

[dotlambda]

Motivation for this change

Even though probably not many people use ddar anymore, I think we have a responsibility towards the users and someone not being able to access their ddar backup seems like something to care about. Because ddar is broken on master, I've gone ahead and fixed the expression.
I don't know if it's okay to move it out of pythonPackages, but it doesn't belong there as its not a library and it doesn't work with Python 3 anyway.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

---

/cc @viric

[GrahamcOfBorg]

Success on x86_64-linux (full log)

Partial log (click to expand)

  it_stores_from_a_file_with_a_name:               [PASS]
  it_deletes_a_member_in_the_middle_of_the_archive: [PASS]
  it_does_not_delete_used_blocks:                  [PASS]
  it_will_not_shell_out_for_source:                [PASS]
yes: standard output: Broken pipe
=========================================================
Tests:   10 | Passed:  10 | Failed:   0
/nix/store/a6dmjklp36kl3ia3vb370dv0nszhx2hn-ddar-1.0
/nix/store/hpd1gcf4isx330gh5bacw5yfwigblbdc-roundup-0.0.6
/nix/store/ldliih4bikksk965kmkrzr65xwvhkddq-shocco-1.0

[GrahamcOfBorg]

Success on aarch64-linux (full log)

Partial log (click to expand)

  it_stores_from_a_file_with_a_name:               [PASS]
  it_deletes_a_member_in_the_middle_of_the_archive: [PASS]
  it_does_not_delete_used_blocks:                  [PASS]
  it_will_not_shell_out_for_source:                [PASS]
=========================================================yes: standard output: Broken pipe

Tests:   10 | Passed:  10 | Failed:   0
/nix/store/h7f9f42iyxw4dh215yhwplybz2zwd431-ddar-1.0
/nix/store/0lg5rfv45kizwhnpddp7lyvh2qz2p89v-roundup-0.0.6
/nix/store/wqadsavyl3kqn6pd7g52qvy5sssdp7b6-shocco-1.0