feat: add (de)serialize to BalancedBinaryMerkleTree (#5744)

Description
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Add (de)serialize traits to `BalancedBinaryMerkleTree`

Motivation and Context
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This is needed for caching the `BalancedBinaryMerkleTree` per epoch.

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Breaking Changes
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- [x] None
- [ ] Requires data directory on base node to be deleted
- [ ] Requires hard fork
- [ ] Other - Please specify

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base_layer/mmr/src/balanced_binary_merkle_tree.rs

@@ -23,6 +23,7 @@
 use std::{convert::TryFrom, marker::PhantomData};
 
 use digest::Digest;
+use serde::{Deserialize, Serialize};
 use tari_common::DomainDigest;
 use thiserror::Error;
 
@@ -46,7 +47,7 @@ pub enum BalancedBinaryMerkleTreeError {
 // Because this implementation relies on the caller to hash leaf nodes, it is possible to instantiate a tree that is
 /// susceptible to second-preimage attacks. The caller _must_ ensure that the hashers used to pre-hash leaf nodes and
 /// instantiate the tree cannot produce collisions.
-#[derive(Debug)]
+#[derive(Debug, Serialize, Deserialize)]
 pub struct BalancedBinaryMerkleTree<D> {
     hashes: Vec<Hash>,
     _phantom: PhantomData<D>,