QR-based signing flow payloads in Miniscript context

[pyth]

Hi all,
I just published a post on Delving Bitcoin proposing a concrete set of
payloads for QR-based signing flowsin miniscript context::

https://delvingbitcoin.org/t/qr-based-signing-flow-payloads-in-miniscript-context/2464

The post defines the *content* of payloads and is intentionally
agnostic about the wire format, framing, and chunking.

Feedback very welcome, especially from people working on signing
devices or wallets/coordinators that already support, or are planning
to support, Miniscript.

Pyth