feat(cmd/gno): re-use teststore in lint

[thehowl]

continuing the work of #3119.

this PR makes gno lint re-use the same test.Store, speeding up execution (especially on the CI, which lints all packages) by not needing to load all packages for each package that is linted.

[Gno2D2]

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[codecov]

Codecov Report

Attention: Patch coverage is 74.72527% with 23 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
gnovm/cmd/gno/lint.go	72.41%	6 Missing and 2 partials ⚠️
gnovm/pkg/gnomod/pkg.go	30.00%	5 Missing and 2 partials ⚠️
gnovm/pkg/packages/imports.go	81.81%	4 Missing ⚠️
gnovm/pkg/doc/dirs.go	57.14%	3 Missing ⚠️
gnovm/pkg/test/filetest.go	88.88%	0 Missing and 1 partial ⚠️

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[gfanton]

On my machine, linting the entire example folder, I went from 2m20s to 8s ... 🚀 🤩

cc @zivkovicmilos