Fix QCoDeSDeprecation warning

[shumpohl]

src\tests\mapping_test.py triggers a QCoDeS deprecation warning due to the broken and deprecated __getitem__ implementation.

This PR rewrites the function that recurses through instruments to find aall parameters by clearly checking for iterability instead of attempting it.

The alternative to silence the warning because we accidentally trigger it and catch the caused exception anyways.

TODO:

• Test that the current implementation handles InstrumentChannel and ChannelTuple

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.

Project coverage is 22.30%. Comparing base (6f1694a) to head (71b316e).

Files with missing lines	Patch %	Lines
src/qumada/instrument/mapping/base.py	90.90%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #154      +/-   ##
==========================================
+ Coverage   22.26%   22.30%   +0.04%     
==========================================
  Files          38       38              
  Lines        4703     4703              
==========================================
+ Hits         1047     1049       +2     
+ Misses       3656     3654       -2     

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[github-actions]

Test Results

  4 files  ±0    4 suites  ±0   13s ⏱️ +3s
 25 tests ±0   25 ✅ ±0  0 💤 ±0  0 ❌ ±0 
100 runs  ±0  100 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 71b316e. ± Comparison against base commit 6f1694a.