Cannot create 1 of n group

https://github.com/BlockchainCommons/bc-sskr/blob/master/src/encoding.c#L131

Is there a reason why 1 of 2, 1 of 3, etc groups are not legal?

Start at src/encoding.c around line 131 and inspect how the group threshold and share count are validated. Determine whether 1-of-n groups are intentionally rejected or should be supported, then define the expected behavior and verify it with relevant tests if present. Done means the issue has a clear rationale and an agreed behavior for 1-of-2, 1-of-3, and similar groups.

Written by the indexing model from the issue text.