Provides a DST, and associated metadata as beneficial.
Also utilizes MuSig's context to session-bind. Since set_keys_messages also
binds to set, this is semi-redundant, yet that's appreciated.
It originally wasn't an enum so software which had yet to update before an
integration wouldn't error (as now enums are strictly typed). The strict typing
is preferable though.
Writes a custom unsigned extrinic creator due to subxt having an internal error
with the scale metadata. While the code in our scope increased, it's much more
ergonomic to our usage. We may end up rewriting most of subxt, eventually.
