EIP-7594: Passive sampling

[ppopth]

Since a node doesn't know when it should request the samples from its peers, it's better to passively receive them from the subnets, so that the node doesn't have to guess when to request the samples. This method is called "passive sampling"

The former method, now called "active sampling", will be used only if the node wants to do sampling in the past slots or the passive sampling fails.