expose required builds and substitutes

[Mic92]

This allows for more interesting build scheduling.

[Mic92]

nix-shell-env % ./src/nix-eval-jobs --gc-roots-dir /tmp/root --impure --check-cache-status --force-recurse --flake .#packages.x86_64-linux.package-with-deps | jq
warning: unknown setting 'allowed-users'
warning: unknown setting 'trusted-users'
path '/home/joerg/git/nix-eval-jobs/build' does not contain a 'flake.nix', searching up
{
  "attr": "",
  "attrPath": [],
  "cacheStatus": "notBuilt",
  "drvPath": "/nix/store/9404n8q0sczpabca39gj0l8yd8612nl1-package-with-deps.drv",
  "inputDrvs": {
    "/nix/store/6sn8q8ssw50vvski2mifkyl8fqjjhbzs-stdenv-linux.drv": [
      "out"
    ],
    "/nix/store/ajyjyxv7h6syp806k4wbk032zh98gmfi-dep-a.drv": [
      "out"
    ],
    "/nix/store/c3pxij9ivzj8b6zqv4sadbcwl6iglc9v-dep-b.drv": [
      "out"
    ],
    "/nix/store/lvnmaggm7nb8nndjps5lkmmcig0spdrr-bash-5.2p32.drv": [
      "out"
    ]
  },
  "isCached": false,
  "name": "package-with-deps",
  "neededBuilds": [
    "/nix/store/ajyjyxv7h6syp806k4wbk032zh98gmfi-dep-a.drv",
    "/nix/store/c3pxij9ivzj8b6zqv4sadbcwl6iglc9v-dep-b.drv",
    "/nix/store/9404n8q0sczpabca39gj0l8yd8612nl1-package-with-deps.drv"
  ],
  "neededSubstitutes": [],
  "outputs": {
    "out": "/nix/store/0algx0219hm8jyg8hjxqilklbfgldkah-package-with-deps"
  },
  "system": "x86_64-linux"
}

[Mic92]

cc @Ericson2314 for review