fix(coverage): expand coverage with -coverpkg

[gfanton]

Addresses #3003.

Following #3003 (comment). This PR expands coverage using -coverpkg. It's a generic and alternative approach compared to #3088.

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.67%. Comparing base (9129e4e) to head (d5470fa).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3089      +/-   ##
==========================================
+ Coverage   63.34%   66.67%   +3.33%     
==========================================
  Files         548      548              
  Lines       78652    78652              
==========================================
+ Hits        49822    52444    +2622     
+ Misses      25470    22805    -2665     
- Partials     3360     3403      +43     

Flag	Coverage Δ
contribs/gnodev	61.16% <ø> (ø)
contribs/gnofaucet	14.82% <ø> (ø)
gno.land	73.62% <ø> (+6.48%)	⬆️
misc/genstd	79.72% <ø> (ø)
tm2	68.69% <ø> (+6.28%)	⬆️

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