Constant yamf_hash::MAX_YAMF_HASH_SIZE

pub const MAX_YAMF_HASH_SIZE: usize = BLAKE2B_HASH_SIZE + 2; // 0x0000_0000_0000_0042usize

The maximum number of bytes this will use for any variant.

This is a bit yuck because it knows the number of bytes varu64 uses to encode the BLAKE2B_HASH_SIZE and the BLAKE2B_NUMERIC_ID (2). This is unlikely to cause a problem until there are hundreds of variants.