Issue summary

• In parity's TrieDb they define a TrieCache that caches the in memory instantiated types for each node.
• Our current cache.TrieCache interface only caches the bytes retrieved from storage and will require decoding into the Go node types.
• I determined that we should update TrieDB to adopt the same node level caching strategy to achieve similar performance.
• Implementation of this new TrieCache interface is actually done in substrate. Integration of the new TrieCache interface into TrieDB will be required.

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