Add support for 'nfc' and 'xpub' commands

[notmandatory]

Description

Add support for the 'nfc' and 'xpub' commands in the lib, cli, and ffi bindings. Updates cli sign for TAPSIGNER and SATSCHIP to sign a PSBT instead of a message.

Closes: #16
Closes: #17

Notes to the reviewers

This is based on #46 and I'll rebase after that PR is merged.

Changelog notice

• Add support for nfc and xpub commands in the lib, cli, and ffi bindings.
• Change cli sign command for TAPSIGNER and SATSCHIP to sign a PSBT instead of a digest.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature