This commit adds `TxPublisher` which implements `Bumper` interface. This
is part one of the implementation that focuses on implementing the
`Broadcast` method which guarantees a tx can be published with
RBF-compliant. It does so by leveraging the `testmempoolaccept` API,
keep increasing the fee rate until an RBF-compliant tx is made and
broadcasts it.
This tx will then be monitored by the `TxPublisher` and in the following
commit, the monitoring process will be added.
This commit adds the method `MaxFeeRateAllowed` to calculate the max fee
rate. The caller may specify a large MaxFeeRate value, which cannot be
cover by the budget. In that case, we default to use the max feerate
calculated using `budget/weight`.
This commit adds a new interface, `Bumper`, to handle RBF for a given
input set. It's responsible for creating the sweeping tx using the input
set, and monitors its confirmation status to decide whether a RBF should
be attempted or not.
We leave implementation details to future commits, and focus on mounting
this `Bumper` interface to our sweeper in this commit.
