Payments weren't properly selected, as it'd drain a sequential series
instead of the specified set, and inputs had a memory condition Rust
couldn't prove was safe.
Modifies FROST behavior so group_key has the offset applied regardless
of if view was called. The unaltered secret_share and
verification_shares (as they have differing values depending on the
signing set) are no longer publicly accessible.
While it was fine as-is, as it only had one variable length property,
this is a bit more robust. Also binds the Curve ID, which should declare
differently even for just different basepoints, and therefore adds two
variable length properties (justifying the transcript).
