Recently we changed the names of some locktime types but kept aliases to
the original names. To assist with ongoing maintenance lets use the new
names already.
Internal change only.
Parsing and displaying strings is a PITA. `FeeRate` is likely not that
heavily used at the moment and users can always just call
`to_sat_per_kwu()` to format it.
So we can get the `units-1.0-alpha.0` release out the door just remove
the `Display` and `FromStr` impls for now. They can be added back in
later when we have time to get #4339 in.
The existing display regression tests only tested height locktimes.
Denomination display regression and round trip were not tested.
Add tests for time locktimes and denomination.
Existing display tests only test lock by block height. New tests are
needed for lock by block time.
Change existing test names to make it clear which type of locktime is
being tested.