Add PoolStateMachine.ConnectionGroup (#425)

[fabianfett]

No description provided.

[codecov-commenter]

Codecov Report

Merging #426 (71774a9) into main (20a8c34) will increase coverage by 1.04%.
The diff coverage is 72.45%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #426      +/-   ##
==========================================
+ Coverage   56.99%   58.03%   +1.04%     
==========================================
  Files         119      120       +1     
  Lines        8410     8843     +433     
==========================================
+ Hits         4793     5132     +339     
- Misses       3617     3711      +94     

Files	Coverage Δ
Sources/ConnectionPoolModule/Max2Sequence.swift	100.00% <100.00%> (ø)
...ources/ConnectionPoolModule/PoolStateMachine.swift	16.66% <ø> (+16.66%)	⬆️
...nPoolModule/PoolStateMachine+ConnectionGroup.swift	82.36% <82.36%> (ø)
...nPoolModule/PoolStateMachine+ConnectionState.swift	69.72% <42.10%> (-7.10%)	⬇️

... and 2 files with indirect coverage changes