Fix incorrect placement of z-errors

[pehamTom]

Description

Due to a missing check in the propagation of errors, some Z-errors were propagated incorrectly

Checklist:

• [x] The pull request only contains commits that are related to it.
• [x] I have added appropriate tests and documentation.
• [x] I have made sure that all CI jobs on GitHub pass.
• [x] The pull request introduces no new warnings and follows the project's style guidelines.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.7%. Comparing base (172a381) to head (f9d9baa). Report is 1 commits behind head on main.

Additional details and impacted files

[](https://app.codecov.io/gh/cda-tum/mqt-qecc/pull/272?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum) ```diff @@ Coverage Diff @@ ## main #272 +/- ## ===================================== Coverage 82.6% 82.7% ===================================== Files 46 46 Lines 3920 3978 +58 Branches 353 353 ===================================== + Hits 3241 3292 +51 - Misses 679 686 +7 ``` | [Flag](https://app.codecov.io/gh/cda-tum/mqt-qecc/pull/272/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum) | Coverage Δ | | *Carryforward flag | |---|---|---|---| | [cpp](https://app.codecov.io/gh/cda-tum/mqt-qecc/pull/272/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum) | `83.3% <ø> (ø)` | | Carriedforward from [172a381](https://app.codecov.io/gh/cda-tum/mqt-qecc/commit/172a3818648d30ae625c2b1c4ac42200eb9fc177?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum) | | [python](https://app.codecov.io/gh/cda-tum/mqt-qecc/pull/272/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum) | `82.3% <100.0%> (+0.1%)` | :arrow_up: | | *This pull request uses carry forward flags. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum) to find out more. | [Files](https://app.codecov.io/gh/cda-tum/mqt-qecc/pull/272?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum) | Coverage Δ | | |---|---|---| | [src/mqt/qecc/ft\_stateprep/state\_prep.py](https://app.codecov.io/gh/cda-tum/mqt-qecc/pull/272?src=pr&el=tree&filepath=src%2Fmqt%2Fqecc%2Fft_stateprep%2Fstate_prep.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum#diff-c3JjL21xdC9xZWNjL2Z0X3N0YXRlcHJlcC9zdGF0ZV9wcmVwLnB5) | `72.1% <100.0%> (+0.4%)` | :arrow_up: | ... and [7 files with indirect coverage changes](https://app.codecov.io/gh/cda-tum/mqt-qecc/pull/272/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum)

[pehamTom]

I am currently refactoring code anyway since I am working on something new that overlaps a lot with the state prep functionality. Gonna get rid of those private accesses then.