Running into a chicken-and-egg problem with calculating fees for unsigned PSBT transactions: to calculate the fee, I need the virtual size of the transaction (let's say I have the fee rate in sats/vB from a 3PBP). To calculate the virtual size of the transaction I need the finalized transaction with change output...which requires knowing the fee.The only solution I can think of is signing a dummy PSBT with a dummy change output, get the virtual size, then sign the real PSBT with the proper change output. This seems cumbersome as I'd have to sign multiple PSBTs every time I want to send some Bitcoin.Is there a better way to do this?