Improve test suite speed

[pedro-stanaka]

Summary

Using t.Parallel to speed up tests and also creating a faster make target to test locally (running all tests, but using build caches). Also, pulling some of data creation on tests outside so we can avoid generating a lot of data without reason.

Having faster test suit improves feedback loop and CI times.

The native histogram tests are still taking an awful amount of time, but I did not had time to take a look into extracting data creation.

On main I get:

      329.71 real       411.05 user        37.16 sys

On my branch I get:

       80.68 real       434.55 user        90.90 sys

without racing it is a much better:

real    0m13.486s    user    0m48.597s   sys     0m4.594s

Changes

• test speedup
• Improving test speed by using parallel testing
• Adding target to test without race detector
• The export in the makefile had no side-effects

[MichaHoffmann]

Awesome, this is great! Thanks

$ time go test .
ok      github.com/thanos-io/promql-engine/engine   30.370s

This usually takes 120s on main for me