feature: Allow gui to be None

[evvaaaa]

For supporting DiamondLightSource/fastcs#142

[codecov]

Codecov Report

❌ Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.82%. Comparing base (d587a48) to head (f72a3d6).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fastcs_pandablocks/__init__.py	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #11      +/-   ##
==========================================
+ Coverage   37.78%   37.82%   +0.04%     
==========================================
  Files          13       13              
  Lines         921      920       -1     
==========================================
  Hits          348      348              
+ Misses        573      572       -1     

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