Integrate message bus

[christoph-blessing]

This PR fully transitions the project to using a message bus and handlers handling domain commands and events.

[codecov]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (ba9e0bb) 98.32% compared to head (eed964d) 96.78%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #53      +/-   ##
==========================================
- Coverage   98.32%   96.78%   -1.54%     
==========================================
  Files          24       25       +1     
  Lines         894      840      -54     
  Branches      109       99      -10     
==========================================
- Hits          879      813      -66     
- Misses          8       16       +8     
- Partials        7       11       +4     

Files	Coverage Δ
link/adapters/controller.py	100.00% <100.00%> (ø)
link/adapters/gateway.py	100.00% <100.00%> (ø)
link/adapters/present.py	100.00% <100.00%> (ø)
link/domain/commands.py	100.00% <100.00%> (ø)
link/domain/events.py	100.00% <100.00%> (ø)
link/service/gateway.py	100.00% <100.00%> (ø)
link/service/handlers.py	100.00% <100.00%> (ø)
link/service/uow.py	100.00% <100.00%> (ø)
link/infrastructure/link.py	95.23% <93.33%> (-2.14%)	⬇️
link/domain/link.py	94.44% <91.30%> (-2.86%)	⬇️
... and 2 more

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