better NetworkProvider/ElectrumNetworkProvider error types

[mr-zwets]

two network provider errors for consensus valid transactions can be txn-mempool-conflict and min relay fee not met (code 66)

currently the network provider just errors but people might want to handle these errors in specific ways client side if they can get an easy error type

[mainnet-pat]

Also there is an error for inputs already spent in concurrent environments. like cauldron trades