Improve storing model values and cached defaults

[dmach]

No description provided.

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (c86093b) 31.05% compared to head (b8d6c94) 31.07%.
Report is 3 commits behind head on master.

Files	Patch %	Lines
osc/build.py	0.00%	6 Missing ⚠️
osc/util/packagequery.py	0.00%	3 Missing ⚠️
osc/util/models.py	96.29%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1462      +/-   ##
==========================================
+ Coverage   31.05%   31.07%   +0.01%     
==========================================
  Files          49       49              
  Lines       17758    17779      +21     
==========================================
+ Hits         5514     5524      +10     
- Misses      12244    12255      +11     

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