fix!: Tidy up types related to test report

[louis-z]

There was confusion regarding test reports, test report summaries and their deserialization. Let's fix it.

Here is an example of a test report summary:

{
  "total": {
    "time": 675.9024454999998,
    "count": 1342,
    "success": 1268,
    "failed": 0,
    "skipped": 74,
    "error": 0,
    "suite_error": null
  },
  "test_suites": [
    {
      "name": "ui_tests",
      "total_time": 528.3635450999999,
      "total_count": 306,
      "success_count": 232,
      "failed_count": 0,
      "skipped_count": 74,
      "error_count": 0,
      "build_ids": [
        152323548,
        152323551,
        152323554,
        152323555,
        152333647
      ],
      "suite_error": null
    },
    {
      "name": "unit_tests",
      "total_time": 147.5389003999998,
      "total_count": 1036,
      "success_count": 1036,
      "failed_count": 0,
      "skipped_count": 0,
      "error_count": 0,
      "build_ids": [
        152323547
      ],
      "suite_error": null
    }
  ]
}

and an excerpt from its associated test report:

{
  "total_time": 675.9024454999998,
  "total_count": 1342,
  "success_count": 1268,
  "failed_count": 0,
  "skipped_count": 74,
  "error_count": 0,
  "test_suites": [
    {
      "name": "unit_tests",
      "total_time": 147.5389003999998,
      "total_count": 1036,
      "success_count": 1036,
      "failed_count": 0,
      "skipped_count": 0,
      "error_count": 0,
      "suite_error": null,
      "test_cases": [
        {
          "status": "success",
          "name": "GitFetcherTests.Test_FetchRemoteBranch_detects_corrupted_git_folder",
          "classname": "MyApp.Tests.Git.GitFetcherTests",
          "file": null,
          "execution_time": 7.48497,
          "system_output": null,
          "stack_trace": null,
          "recent_failures": null
        },
        ...
      ]
    },
    {
      "name": "ui_tests",
      "total_time": 528.3635451,
      "total_count": 306,
      "success_count": 232,
      "failed_count": 0,
      "skipped_count": 74,
      "error_count": 0,
      "suite_error": null,
      "test_cases": [
        {
          "status": "success",
          "name": "GitTests.SubRepositories_are_displayed",
          "classname": "MyApp.UI.Tests.Git.GitTests",
          "file": null,
          "execution_time": 30.034155,
          "system_output": null,
          "stack_trace": null,
          "recent_failures": null
        },
        ...
      ]
    }
  ]
}