fix(validate): compute slot / time conversion correctly

[scarmuega]

To correctly execute time / slot conversions we need the whole history of the chain eras. Instead of simple values in the PParams struct, we need a new struct that represents the history, similar to what Dolos has here: https://github.com/txpipe/dolos/blob/main/src/ledger/pparams/summary.rs

Decide if maybe we just migrate Dolos' pparams module to Pallas.

[Quantumplation]

We just recently wrote something like that for Amaru:

pragma-org/amaru#39