refactor(tests): join directories files and files2

[thehowl]

Some slight refactoring in tests/file.go to also make the code clearer in file_test.go (ie. make it clear in code that the difference is WithNativeLibs, which may be less obvious if this is through a boolean flag).

Merging the directories was done taking a look at git diff --no-index files files2, after a first inspection of the differing files by doing a sha1sum **/*.gno in each directory. For reference, here is the diff of sha sums in the two directories, highlighting extra and different files in each directory (- is files/, + is files2) together with a few comments on their effective differences.

In many cases, the differences are attributed to formatting differences in the time package. I'm not sure what is the full background on these, but in any case I kept doing any changes on them as outside of the scope of the PR.

In the new merged directory, where tests diverge or are specific to either stdlibs or native, they should contain _native or _stdlibs

[zivkovicmilos]

Looks great 💯

It's much more cleaner now. I love the touch with the run options 👌

I've left a few small comments that we can discuss