Longer distance evaluation period

https://forum.duniter.org/t/besoin-de-plus-de-forgeron-avec-oracle-de-distance/12669/22?u=tuxmain

Also clarify evaluation's behavior in documentation.

It seems illusory for now to target a high proportion of oracles among validators. Ğtest doesn't need ultra-low success rate so 40 blocks should be a good tradeoff, but I would still advocate for 100 blocks in Ğ1.