🚸 Allow indexed registers as operation arguments

[burgholzer]

Description

This update enables the use of indexed registers as arguments for operations.
For example, in Python:

from mqt.core.ir import QuantumComputation

qc = QuantumComputation()
q = qc.add_qubit_register(2)
c = qc.add_classical_register(2)

qc.h(q[0])
qc.cx(q[0], q[1])
qc.measure(q[0], c[0])
qc.measure(q[1], c[1])

In C++:

#include "ir/QuantumComputation.hpp"

auto qc = qc::QuantumComputation();
const auto& q = qc.addQubitRegister(2);
const auto& c = qc.addClassicalRegister(2);

qc.h(q[0]);
qc.cx(q[0], q[1]);
qc.measure(q[0], c[0]);
qc.measure(q[1], c[1]);

This improvement expands the usability of the IR as it no longer requires users to track the order in which registers were added to infer their qubits' indices.

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

Attention: Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.3%. Comparing base (34f2bfb) to head (eb4c786).
Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
include/mqt-core/ir/Register.hpp	83.3%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #839   +/-   ##
=====================================
  Coverage   92.3%   92.3%           
=====================================
  Files        127     127           
  Lines      13509   13520   +11     
  Branches    2080    2081    +1     
=====================================
+ Hits       12471   12487   +16     
+ Misses      1038    1033    -5     

Flag	Coverage Δ
cpp	92.0% <91.6%> (+<0.1%)	⬆️
python	99.7% <ø> (ø)

Files with missing lines	Coverage Δ
include/mqt-core/ir/QuantumComputation.hpp	100.0% <ø> (ø)
src/ir/QuantumComputation.cpp	92.5% <100.0%> (+<0.1%)	⬆️
include/mqt-core/ir/Register.hpp	91.6% <83.3%> (-1.7%)	⬇️

... and 5 files with indirect coverage changes