Fix/systems report domain count

[noamblitz]

Changes

Fixes a bug where sometimes domains were counted double. Also added a unit test that checks for this bug and some other tests.

Issue link

Closes #2471

Demo

Please add some proof in the form of screenshots or screen recordings to show (off) new functionality, if there are interesting new features for end-users.

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Code Checklist

• All the commits in this PR are properly PGP-signed and verified.
• This PR only contains functionality relevant to the issue; tickets have been created for newly discovered issues.
• I have written unit tests for the changes or fixes I made.
• For any non-trivial functionality, I have added integration and/or end-to-end tests.
• I have performed a self-review of my code and refactored it to the best of my abilities.

Communication

• I have informed others of any required .env changes files if required and changed the .env-dist accordingly.
• I have made corresponding changes to the documentation, if necessary.
• I have included comments in the code to elaborate on what is not self-evident from the code itself, including references to issues and discussions online, or implicit behavior of an interface.

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Checklist for code reviewers:

Copy-paste the checklist from the docs/source/templates folder into your comment.

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Checklist for QA:

Copy-paste the checklist from the docs/source/templates folder into your comment.

[underdarknl]

This looks valid to me.

[stephanie0x00]

Checklist for QA:

• I have checked out this branch, and successfully ran a fresh make reset.
• I confirmed that there are no unintended functional regressions in this branch:
  • I have managed to pass the onboarding flow
  • Objects and Findings are created properly
  • Tasks are created and completed properly
• I confirmed that the PR's advertised feature or hotfix works as intended.

What works:

Looks good. Identified a bug, but that's on main. See ticket #2503.

What doesn't work:

n/a

Bug or feature?:

Identified bug #2503 but that is not related to this PR as it is on the main branch.