✨ Add support for OpenQASM 3.0 else

[martin-fink]

Description

This PR adds support for the else branch in if statements when parsing OpenQASM 3.0.

Example:

if (c == 1) {
  x q[1];
} else {
  x q[0];
  x q[1];
}

This is implemented by adding a second ClassicalControlledOperation to the Quantum Computation with a flipped condition.
When dumping the circuit above, the following is printed:

if (c == 1) {
  x q[1];
}
if (c != 1) {
  x q[0];
  x q[1];
}

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.

[burgholzer]

That was quick. Many thanks!
I just added some small little comments. Nothing too major.

I'll also re-run the coverage tests (they seem to be failing more frequently again recently). That's not on us though, but on the codecov service.

[codecov]

Codecov Report

Merging #498 (7261fa3) into main (24f7ee1) will decrease coverage by 0.1%.
The diff coverage is 84.6%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #498     +/-   ##
=======================================
- Coverage   90.8%   90.8%   -0.1%     
=======================================
  Files        127     128      +1     
  Lines      13846   13867     +21     
  Branches    2174    2177      +3     
=======================================
+ Hits       12579   12598     +19     
- Misses      1267    1269      +2     

Flag	Coverage Δ
cpp	90.5% <84.6%> (-0.1%)	⬇️
python	99.7% <ø> (ø)

Files	Coverage Δ
include/operations/ClassicControlledOperation.hpp	96.8% <ø> (ø)
include/parsers/qasm3_parser/Statement.hpp	92.7% <ø> (ø)
src/parsers/QASM3Parser.cpp	90.4% <100.0%> (+0.5%)	⬆️
include/Definitions.hpp	76.4% <0.0%> (-10.2%)	⬇️
...lude/parsers/qasm3_parser/passes/ConstEvalPass.hpp	80.9% <0.0%> (-2.0%)	⬇️
src/parsers/qasm3_parser/Statement.cpp	87.5% <87.5%> (ø)
src/operations/ClassicControlledOperation.cpp	88.5% <85.1%> (-11.5%)	⬇️

... and 2 files with indirect coverage changes

[burgholzer]

Many thanks for the PR. I just updated a few things and optimized the code a little.

The remaining lines are, per definition, uncoverable. So I am ignoring the failing patch coverage check.

[martin-fink]

Thanks!