Remove minerCost or replace with minerFeeRate
currently, minerCost is stored but was intended to be a well-known number that as all other parts of the metadata is immutable and cannot change. Since hte introduction of the multiple fee system it is now possible for the settlement transaction size to be different over time and so this number would not be immutable.
We should consider removing it entirely and let the library provide this number with some sensible feeRate, or add a configurable feeRate so that it is predictable among all peers what to expect.