Specifies the format for displaying envelope digests in tree output.
Ported from bc-envelope-rust/src/format/tree/format/digest.rs
Short format: first 7 hex characters of the digest. This is the default format.
Full format: complete 64 hex character digest.
UR format: digest encoded as a UR string.
Specifies the format for displaying envelope digests in tree output.
Ported from bc-envelope-rust/src/format/tree/format/digest.rs