fix(pkg/doc): ensure mod packages are loaded correctly

[thehowl]

This is the "proper fix" for the issue encountered by @jefft0, @zivkovicmilos, @moul & others, fixed in make test by #1301.

Essentially, because of the way that gno doc handled directories with gno.mod, the cached version of gno.land/p/demo/avl had higher priority than its version in Gnomod.

I've added a txtar integration test to show the behaviour which fails on master and is fixed in this branch.

Fixes #1142.

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
• Added new benchmarks to generated graphs, if any. More info here.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (34d78b3) 47.92% compared to head (d825e2a) 47.90%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1306      +/-   ##
==========================================
- Coverage   47.92%   47.90%   -0.03%     
==========================================
  Files         372      372              
  Lines       62990    63007      +17     
==========================================
- Hits        30187    30181       -6     
- Misses      30344    30364      +20     
- Partials     2459     2462       +3     

Files	Coverage Δ
gnovm/pkg/doc/dirs.go	86.20% <91.30%> (+0.21%)	⬆️

... and 4 files with indirect coverage changes

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[thehowl]

There are some questions I've raised myself about this implementation and in general about how to manage static analysis tools, gno.mod and dependencies. I started writing a wall of text here outlining the problem, coming up with a proposal, and deciding this needs another issue.

In any case, I've put this back into a draft while we clarify some issues. Expect an issue relating to this PR soon.

[thehowl]

Current state: there is a crucial problem which has stung us time and time again in cmd/gno, which is that there is no current centralised way within the gno command to answer the question "If I have an import path x, which paths should I look to try to resolve this dependency and in which order should they be?".

There are also some related concerns on how, at the current state of gno development, we can manage having code which has the same import path but is on a different chain; ie. test3 vs. portal-loop. A proposal on how to solve this has been added in #1352.

All in all, this PR addresses an issue which likely should really be fixed with a v2 of #1299. I'll make another comment there, mark it as draft and close this PR.