ci: enable all rules for testifylint

[mmorel-35]

This refactors and modernizes test assertions replacing older assertion patterns with more expressive and idiomatic ones from the testify library. It also updates linter configuration for improved code quality checks.

Test assertion improvements:

• Replaced require.Equal(t, true, errors.Is(...)) with require.ErrorIs for clearer error assertion.

Linter configuration:

• Updated .golangci.yml to enable all testifylint checks by default, removing the previous list of disabled checks. This ensures stricter and more consistent test code quality.

[mmorel-35]

@tonistiigi ,
I have revert len, empty and bool-compare rules as you asked and just focused on the rest of the used methods. This includes ErrorContains, EqualError use instead of err.Error() comparisons. require.Error has been drop for thoses cases as thoses are already checking for non nil errors