Change the type of minFeeRefScriptCoinsPerByte

[lehins]

In a recent PR #3983 a new protocol parameter has been added. One oversigt was that the type that was used does not allow for a more fine grain tuning of the fee, because it is backed by an CoinPerByte, which is essentially a Coin. In other words it only allows one lovelace per byte granularity, which might not be enough in the future.

In order to allow us to be as precise as necessary, we need to:

• - We need to change the type to NonNegativeInterval
• - Change the formula to use rounding
• - Rename the parameter to minFeeRefScriptCostPerByte
• - Adjust CDDL

Here is the implementation of the fee calculation:

cardano-ledger/eras/conway/impl/src/Cardano/Ledger/Conway/Tx.hs

Lines 85 to 87 in e73acc6

	alonzoMinFeeTx pp tx <+> (refScriptsSize <×> refScriptFee)
	where
	CoinPerByte refScriptFee = pp ^. ppMinFeeRefScriptCoinsPerByteL

Which should be changed to this new calculation:

 alonzoMinFeeTx pp tx <+> refScriptsFee
 where 
   refScriptFee = unboundRational (pp ^. ppMinFeeRefScriptCoinsPerByteL)
   refScriptsFee = Coin (floor (fromIntegral @Int @Rational refScriptsSize * refScriptFee)) 

[aniketd]

@lehins Thank you for such a detailed write up here ❤️ 🙌 🙇 💪