Small improvments to Keithley drivers

[jenshnielsen]

This improves Keithley drivers to not rely on dynamic non static attributes.

• Replace Qcodes function with methods with a statically known type
• Add parent to instrument channels where required

The does not contain changes 2600 driver to avoid conflict with #7851

Cherry-picked from #7845

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 59.94%. Comparing base (61ced51) to head (9fc3772).
⚠️ Report is 37 commits behind head on main.

Files with missing lines	Patch %	Lines
...codes/instrument_drivers/Keithley/Keithley_2000.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7866      +/-   ##
==========================================
+ Coverage   59.87%   59.94%   +0.07%     
==========================================
  Files         352      352              
  Lines       31872    31933      +61     
==========================================
+ Hits        19083    19143      +60     
- Misses      12789    12790       +1     

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