feat: add support for dynamic user addresses in txtar tests

[deelawn]

This feature makes it possible to reference addresses of users that were dynamically added using the adduser command. The modified adduser.txtar file contains an example of this and the modified doc file contains instructions how to use it.

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: 6 lines in your changes are missing coverage. Please review.

Comparison is base (d1ead00) 55.80% compared to head (1dd23d8) 55.80%.

Files	Patch %	Lines
gno.land/pkg/integration/testing_integration.go	88.46%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1581      +/-   ##
==========================================
- Coverage   55.80%   55.80%   -0.01%     
==========================================
  Files         435      435              
  Lines       66055    66073      +18     
==========================================
+ Hits        36862    36869       +7     
- Misses      26320    26328       +8     
- Partials     2873     2876       +3     

Flag	Coverage Δ
go-1.21.x	∅ <ø> (∅)
misc	∅ <ø> (∅)
misc-_test.genstd	∅ <ø> (∅)

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[thehowl]

@gfanton I'll leave you to do the first review, ping me if you need a second one.

[gfanton]

I'm fine with the code, but I don't really understand why we should use withuser instead of an environment variable, which seems more straightforward to me.

adduser test8
withuser test8 gnokey maketx call -pkgpath gno.land/r/bar -func Render -args 'USERADDRESS' 

vs

adduser test8
gnokey maketx call -pkgpath gno.land/r/bar -func Render -args $ADDRESS_test8

Additionally, withuser doesn't seem very composable and can disrupt copy/paste actions. I'm also concerned that if we start using this kind of command, we might drift away from the original gnokey command usage.

[deelawn]

Thanks @gfanton . You're 100% correct. I forgot it exports this environment variable 🤦‍♂️. Closing this...