fix rigol dg4000 value mappings

[konosubakonoakua]

fix value mappings

[konosubakonoakua]

DG4000 cannot be upgraded with an arbitrary U disk.

I have consulted with Rigol Tech support, They said it's better to send my device to them.
Their engineer can do the upgrade. However, I don't have time to wait for that.
IMO, I should leave this PR open in case someone else have encountered the same issue.

[konosubakonoakua]

@jenshnielsen I have restore the parser to int, please review again.

[jenshnielsen]

@konosubakonoakua Should be good to go, just waiting on clarity on the last question inline

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Please upload report for BASE (main@5d9afec). Learn more about missing BASE report.
Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
...rc/qcodes/instrument_drivers/rigol/Rigol_DG4000.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6345   +/-   ##
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  Coverage        ?   67.34%           
=======================================
  Files           ?      352           
  Lines           ?    32139           
  Branches        ?        0           
=======================================
  Hits            ?    21645           
  Misses          ?    10494           
  Partials        ?        0           

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