init geth t8n kzg on demand only

[winsvega]

Rationale

With recent kzg introduction some kzg logic gets initiated with each t8n call that significantly reduce the performance on all the tests that doesn't need it

Implementation

Investigate if it's possible to run kzg startup logic in t8n only on those tests that request it. (Ex. 4844 tests)

[karalabe]

This is fixed on master

[karalabe]

I mean it was never broken on master AFAIK, only for --ckzg

[karalabe]

I guess some milliseconds/tenst/hundreds may be wasted on a geth startup, that shouldn't hit t8n tho'?

[winsvega]

yes running the tests with geth t8n now 6000 seconds vs 2500 previously