Add support for Waveshare Modbus Relays

[ep1cman]

Waveshare only implement the ability to query the status of all relays (https://www.waveshare.com/wiki/Modbus_RTU_Relay#Read_States_of_Relays) not just one, so a modification to the existing drivers is required.

Checklist

• Documentation for the feature
• Tests for the feature

• The arguments and description in doc/configuration.rst have been updated

• Add a section on how to use the feature to doc/usage.rst

• Add a section on how to use the feature to doc/development.rst

• PR has been tested

• Man pages have been regenerated

[codecov]

Codecov Report

Attention: Patch coverage is 46.15385% with 14 lines in your changes missing coverage. Please review.

Project coverage is 56.2%. Comparing base (fff35ee) to head (60e5af1).

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
labgrid/driver/modbusdriver.py	41.1%	10 Missing ⚠️
labgrid/remote/client.py	0.0%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1575     +/-   ##
========================================
- Coverage    56.2%   56.2%   -0.1%     
========================================
  Files         170     170             
  Lines       13248   13271     +23     
========================================
+ Hits         7449    7460     +11     
- Misses       5799    5811     +12     

Flag	Coverage Δ
3.10	56.2% <46.1%> (-0.1%)	⬇️
3.11	56.2% <46.1%> (-0.1%)	⬇️
3.12	56.2% <46.1%> (-0.1%)	⬇️
3.13	56.1% <46.1%> (-0.1%)	⬇️
3.9	56.2% <46.1%> (-0.1%)	⬇️

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