Solis wifistick alternative approach

[mvdwetering]

This is an alternative approach to the changes in PR #55.

Instead of not allowing a session to be provided it will now use the provided session or create a session for one time use.

Note that I don't really like the big try/finally block, but it seemed better than putting callse to close() all over the place which is errorprone.

[codecov]

Codecov Report

Merging #95 (e2eeaca) into main (95f76da) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #95   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines          181       188    +7     
  Branches        35        38    +3     
=========================================
+ Hits           181       188    +7     

Impacted Files	Coverage Δ
omnikinverter/models.py	100.00% <100.00%> (ø)
omnikinverter/omnikinverter.py	100.00% <100.00%> (ø)

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[mvdwetering]

It was a bit tricky because the codepath is only triggered when there is a session active, so during a request, but I have it covered now.

[klaasnicolaas]

Test with another inverter and made a few more minor changes, ready for merging!