Fix typechecking with newest qcodes and Numpy

[jenshnielsen]

With newer versions of qcodes the typing of ChannelList has improved to reflect that __getitem__ always returns a InstrumentChannel when called with an int so this cast is now redundant

Numpy has become significantly more strict uncovering a few issues

[jenshnielsen]

@jpsecher For the QDAC2 this method was typed as returning a sequence but does actually return a numpy array

Unfortunately numpy arrays are currently not considered sequences see numpy/numpy#2776

Do you have a preference if the type signature should change like I have done here or we should convert the output to a list

[jenshnielsen]

@sldesnoo-Delft @eendebakpt

Numpy 1.22 triggers a type checking error in the m4i driver related to from buffer. Since I don't have much context on this driver I have silenced the warning here but perhaps you want to look into a better fix?

[codecov-commenter]

Codecov Report

Merging #116 (31430f4) into master (b6b5a6c) will increase coverage by 0.03%.
The diff coverage is 64.28%.

@@            Coverage Diff             @@
##           master     #116      +/-   ##
==========================================
+ Coverage   19.81%   19.85%   +0.03%     
==========================================
  Files         121      121              
  Lines       14703    14709       +6     
==========================================
+ Hits         2914     2920       +6     
  Misses      11789    11789              

Impacted Files	Coverage Δ
...trib_drivers/drivers/NationalInstruments/Switch.py	0.00% <0.00%> (ø)
qcodes_contrib_drivers/drivers/Spectrum/M4i.py	34.84% <0.00%> (ø)
qcodes_contrib_drivers/drivers/QDevil/QDAC2.py	96.33% <100.00%> (ø)
...ontrib_drivers/tests/QDevil/test_sim_qdac2_init.py	100.00% <100.00%> (ø)

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[sldesnoo-Delft]

I will have a look at the M4i driver. This week I already worked on another fix for the driver.

[sldesnoo-Delft]

I just learned that numpy 1.22 requires Python 3.8. However Python 3.8 is not supported by the older Keysight PXI system drivers and firmware. It requires the latest drivers and firmware that have been released in December 2021.
I've not yet had time to test the new firmware and update the drivers.
This might imply a breaking change for people with older licenses that do not allow an update of the firmware.
Dropping support for Python 3.7 would mean that people have to buy new licenses to be able to upgrade to new firmware and drivers.

What's the policy of qcodes regarding the supported Python versions?

[jpsecher]

@jenshnielsen thanks, the changes to QDAC2.py look fine.

[jenshnielsen]

@sldesnoo-Delft this does not actually drop 3.7 support just yet but just stops type checking with 3.7. We were going to drop 3.7 exactly because numpy, pandas, xarray ipython and so on has dropped support. Could you copy your comment into microsoft/Qcodes#3889 that may be an important datapoint for delaying the dropping of 3.7 but its nice if we can collect all info there.