Make txtar and Codecov play nice (upload coverage)

[zivkovicmilos]

Description

Currently, the monorepo has an abundance of .txtar testing suites, but the code they cover is never uploaded or made aware to Codecov, causing the CI to fail on some PRs even though there is coverage.

This task involves making sure code covered with .txtar tests (which are ran from _test.go files) is visible in Codecov.

DoD:

• CodeCov / go recognizes code ran by .txtar tests
• .txtar code coverage is visible on the Codecov dashboard

Example PR:

• feat: add r/sys/params + params genesis support #3003

[gfanton]

After doing some checks, it appears that the current txtar implementation is correctly handling coverage. The only case where txtar could skip coverage is when it executes a binary in a separate process, where it loses track of coverage, but this has already been addressed (#1243).

The issue in #3003 is not related to txtar but rather to how Go generates coverage by default. See my comment #3003 (comment).

Closing this for now. Feel free to reopen it if you still think there is a problem related to txtar specifically.