Tezt is faster to initialize

The SRS can take some time to compute. We compute it lazily.

It would be better to compute it once though, this patch may introduce some regression.

You can check that the time is after before and after the patch. You can check the problem solved via perf and the following commands:

sudo perf record --call-graph=dwarf -- _build/default/tezt/tests/main.exe basic --list -f basic.ml
sudo hotspot perf.data

We went from 9 seconds to initialize Tezt to 0.4 seconds.

Many thanks to @alocascio for providing the initial patch ;)