d3b8a54a81 Refactor CFeeRate to use FeeFrac internally (Pol Espinasa)
Pull request description:
The `FeeFrac` type represents a fraction, intended to be used for `sats/vbyte` or `sats/WU`. It was added to improve accuracy when evaluating fee rates in cluster mempool. [1]
But it can also be used to fix the precision issues that the current `CFeeRate` class has now.
At the moment, `CFeeRate` handles the fee rate as satoshis per kilovirtualbyte: `CAmount / kvB` using an integer.
This PR fix `CFeeRate` precision issues by encapsulating `FeeFrac` internally keeping backwards compatibility.
This PR can also be used as a based to use multiple units on RPC calls as detailed in this issue [2].
Some previous discussions:
[1] https://github.com/bitcoin/bitcoin/pull/30535
[2] https://github.com/bitcoin/bitcoin/issues/32093
ACKs for top commit:
achow101:
ACK d3b8a54a81
murchandamus:
code review, lightly tested ACK d3b8a54a81
ismaelsadeeq:
re-ACK d3b8a54a81📦
theStack:
Code-review ACK d3b8a54a81
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