* StoreKVPair protobuf message definition and generated go types
* store WriteListener
* update MultiStore, CacheWrap, CacheWrapper interfaces
* adjust KVStores to fit new CacheWrapper interface
* new ListenKVStore
* adjust multistores to fit new MultiStore interface and enable wrapping returned KVStores with the new ListenKVStore
* typo fixes in adr
* ListenKV Store test
* update server mock KVStore and MultiStore
* multistore unit test; fix multistore constructor
* update changelog
* fix bug identified in CI
* improve codecov, minor fixes/adjustments
* review fixes
* review updates; flip set to delete in KVStorePair, updated proto-docs from running 'make proto-gen'
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