🩹 fix endless loop on unsupported operations in OpenQASM gate declarations

[burgholzer]

Description

This PR fixes an endless loop in the OpenQASM parser upon encountering unexpected statements in gate declarations. WIth this PR, the parser actually errors out with an appropriate error message instead of looping forever.

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 92.1%. Comparing base (698af02) to head (b8fd529). Report is 1 commits behind head on main.

Additional details and impacted files

[](https://app.codecov.io/gh/cda-tum/mqt-core/pull/700?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 #700 +/- ## ======================================= - Coverage 92.1% 92.1% -0.1% ======================================= Files 125 125 Lines 13759 13757 -2 Branches 2151 2150 -1 ======================================= - Hits 12673 12671 -2 Misses 1086 1086 ``` | [Flag](https://app.codecov.io/gh/cda-tum/mqt-core/pull/700/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum) | Coverage Δ | | |---|---|---| | [cpp](https://app.codecov.io/gh/cda-tum/mqt-core/pull/700/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum) | `91.8% <100.0%> (-0.1%)` | :arrow_down: | | [python](https://app.codecov.io/gh/cda-tum/mqt-core/pull/700/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum) | `99.7% <ø> (ø)` | | | [Files with missing lines](https://app.codecov.io/gh/cda-tum/mqt-core/pull/700?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/ir/parsers/qasm3\_parser/Parser.cpp](https://app.codecov.io/gh/cda-tum/mqt-core/pull/700?src=pr&el=tree&filepath=src%2Fir%2Fparsers%2Fqasm3_parser%2FParser.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cda-tum#diff-c3JjL2lyL3BhcnNlcnMvcWFzbTNfcGFyc2VyL1BhcnNlci5jcHA=) | `92.6% <100.0%> (-0.1%)` | :arrow_down: |