🩹 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:

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@           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	Coverage Δ
cpp	91.8% <100.0%> (-0.1%)	⬇️
python	99.7% <ø> (ø)

Files with missing lines	Coverage Δ
src/ir/parsers/qasm3_parser/Parser.cpp	92.6% <100.0%> (-0.1%)	⬇️