Improve Amount and remove AmountStr.

[crodas]

          You can just use the `Amount` there no need to wrap it in the `AmoutnStr`. The reason we have to use `AmountStr` is for when the Keys response is json serialized it needs to be as a string and not an int, so that's really the only place we should use `AmountStr` everywhere else is `Amount`.

EDIT: I see you're creating a Keys which currently does expect the AmountStr

cdk/crates/cashu/src/nuts/nut01/mod.rs

Line 63 in e1458b0

pub fn new(keys: BTreeMap<AmountStr, PublicKey>) -> Self {

. But since whats needed is as i described above we should change this and that can be an amount and we can just create a custom serialize deserilization, that maybe a better way to handle this and then we don't need the AmountStr type?

cc @crodas

Originally posted by @thesimplekid in #605 (comment)