Add table support in pva and fix gui pv naming

[shihab-dls]

#Fixes #166
This PR adds PvaEpicsGui, which allows tables and prepends pva:// to pvs to allow access to pva signals via the GUI. Tables already have this added, so this issue in pvi should be merged.

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 92.28%. Comparing base (aec213b) to head (a37abf2).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fastcs/transport/epics/gui.py	93.93%	2 Missing ⚠️
src/fastcs/transport/epics/pva/adapter.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #167      +/-   ##
==========================================
+ Coverage   92.27%   92.28%   +0.01%     
==========================================
  Files          40       40              
  Lines        1980     2009      +29     
==========================================
+ Hits         1827     1854      +27     
- Misses        153      155       +2     

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[GDYendell]

Just some minor things