cf129ad314 fix: re-implement (de)serialization from/to readers/writers (elsirion)
Pull request description:
Fixes#3250.
The serialization is less than ideal and still allocates a lot. I can understand not wanting to (ab)use the consensus encoding traits, but they have a pretty good interface, copying it and creating some `EncodePsbt` and `DecodePsbt` traits with similar interfaces would have been nice imo.
ACKs for top commit:
Kixunil:
ACK cf129ad314
apoelstra:
ACK cf129ad314 successfully ran local tests; LGTM -- I believe this is non-breaking, as does cargo-semver-checks, so we can backport this to 0.32
Tree-SHA512: d7f218164d772db3a9fb4436953c3b5fd3677b92078d0843233197629df7d852d80615a3ff38c5b70771381ba1aeb30defdc98ee63653e570bb75dc553400cad