Try fix aad

[insipx]

• Import ByteWrapper trait as _ to avoid name conflicts
• implement From<&[u8]>/Vec<u8> for ByteWrapper
• use impl Trait in return position for fn aad

@tuddman and I worked out the errors for the ByteWrapper trait on aad. However, using a generic for ByteWrapper eventually requires that a generic be added to MlsGroup which could create more complication than necessary. There are a few ways forward, but I wanted to gather some context for aad before continuing.

aad is present on MlsGroup in the load method:

    /// Loads the state of the group with given id from persisted state.
    pub fn load<Storage: crate::storage::StorageProvider>(
        storage: &Storage,
        group_id: &GroupId,
    ) -> Result<Option<MlsGroup>, Storage::Error> {
        let group_config = storage.mls_group_join_config(group_id)?;
        let core_group = CoreGroup::load(storage, group_id)?;
        let proposals: Vec<(ProposalRef, QueuedProposal)> = storage.queued_proposals(group_id)?;
        let own_leaf_nodes = storage.own_leaf_nodes(group_id)?;
        let aad = storage.aad(group_id)?;
        let group_state = storage.group_state(group_id)?;
        let mut proposal_store = ProposalStore::new();

        for (_ref, proposal) in proposals {
            proposal_store.add(proposal);
        }

        let build = || -> Option<Self> {
            Some(Self {
                mls_group_config: group_config?,
                group: core_group?,
                proposal_store,
                own_leaf_nodes,
                aad, // <----- this is the last error, but requires MlsGroup<ByteWrapper>
                group_state: group_state?,
            })
        };

        Ok(build())
    }

a simple solution is having a to_vec fn on ByteWrapper but then ByteWrapper itself seems redundant.