MuSig aggregation hides participant keys, so account xpubs do not need
individual trailing derivation.
Specify that encryption uses participant roots rather than the aggregate key.
Add MuSig2 test vectors: one for a bare aggregate and one for aggregate
derivation.
Rename keys_types.json to recipient_keys.json and generalize the format
to support multiple descriptors and multiple recipient keys:
- "key": a single key-expression string becomes "descriptors": an array
of complete descriptor strings.
- "expected": an x-only key string becomes "expected_keys": an array
containing that key; null remains null.
Convert the nine existing cases by wrapping each key expression in tr(),
except the uncompressed literal uses pk(), since tr() does not accept it.
Each case has one descriptor.
Specify that parsing stops immediately. Add a vector with an item followed
by a terminator and ignored bytes.
Clarify that TYPE 0x00 also doesn't require TYPE_LENGTH.
Make change_descriptor explicitly optional for non-multipath descriptors.
Add a receive-only document vector with no change descriptor or optional
metadata; the existing vectors cover a receive/change pair and multipath.
