Allow users to input fractional feerate

[alecalve]

I can input 6 sats or 7 sats but not 6.5 (the replaced tx fee rate is much lower than 6 sats/vB).

It’s especially useful for low feerate txs, if a tx is at 1 sats/vB, currently there’s no choice but to double the fee paid.

[jp1ac4]

Thanks for reporting this issue.

Allowing fractional feerates (for both new spends and RBFs) is certainly feasible and we will consider this for a future release.