Fix doxygen errors

Summary:

Identified via -Wdocumentation

Out-of-sequence backport note: the content of psbtwallet.h was moved to wallet.h in D8097, and the doxygen syntax was fixed in the move

This is a backport of Core PR17945

Test Plan: ninja doc-doxygen

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D8620