774f066879 refactor: Change from u64 to Amount (yancy)
Pull request description:
Separate out refactor commit from https://github.com/rust-bitcoin/rust-bitcoin/pull/3794. Can be merged independently.
ACKs for top commit:
tcharding:
ACK 774f066879
apoelstra:
ACK 774f066879c8ad1af81c7e46b404fa63682a0b4c; successfully ran local tests
Tree-SHA512: 9ec5121d823ee3ec506eee5b5187bd496221bd3576afcaa6daf647099720d87b58b69521f29ae9537f123e2958771bc867b123da3f2ba941cba403a6c98e46de