use new mastodon-only sub dbstorage

[akrherz]

also improves test coverage.

[codecov]

Codecov Report

Patch coverage: 50.00% and project coverage change: +0.89% 🎉

Comparison is base (d212cb4) 36.54% compared to head (2235c71) 37.43%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #69      +/-   ##
==========================================
+ Coverage   36.54%   37.43%   +0.89%     
==========================================
  Files           7        7              
  Lines        1122     1122              
==========================================
+ Hits          410      420      +10     
+ Misses        712      702      -10     

Files Changed	Coverage Δ
src/iembot/util.py	34.96% <50.00%> (+2.22%)	⬆️

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.