Move pubsub module from GORT and add tests

[albireox]

Mainly copied the pubsub module from lvmgort with a few changes to the exchange name and such. Added some tests.

[codecov]

Codecov Report

Attention: Patch coverage is 88.53503% with 18 lines in your changes missing coverage. Please review.

Project coverage is 91.0%. Comparing base (728c47f) to head (de453ff).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lvmopstools/pubsub.py	88.3%	5 Missing and 13 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main     #10     +/-   ##
=======================================
- Coverage   91.8%   91.0%   -0.7%     
=======================================
  Files         10      11      +1     
  Lines        544     698    +154     
  Branches      73      91     +18     
=======================================
+ Hits         499     635    +136     
- Misses        22      27      +5     
- Partials      23      36     +13     

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