Fix networkx adapter

[YamLyubov]

BaseNetworkxAdapter refactored to process parameters of graph nodes correctly.

Also:

• adapter now can restore a list of OptGraphs
• OptunaTuner saves study (g.e. to use it for visualisations via optuna)

[codecov-commenter]

Codecov Report

Merging #160 (aec8c8d) into main (533ab80) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #160      +/-   ##
==========================================
+ Coverage   73.95%   73.99%   +0.04%     
==========================================
  Files         129      129              
  Lines        7647     7656       +9     
==========================================
+ Hits         5655     5665      +10     
+ Misses       1992     1991       -1     

Files Changed	Coverage Δ
golem/core/adapter/adapter.py	90.00% <100.00%> (+0.25%)	⬆️
golem/core/adapter/nx_adapter.py	81.96% <100.00%> (+1.61%)	⬆️
golem/core/tuning/optuna_tuner.py	92.85% <100.00%> (+0.08%)	⬆️
golem/core/tuning/tuner_interface.py	90.67% <100.00%> (+0.07%)	⬆️

... and 3 files with indirect coverage changes