migrate datasource from store.KVStore to datastore.Datastore

[gupadhyaya]

Fixes#620

description of the major change:

• prefix changes from byte array to strings, e.g, []byte{0} to "0". this is required as datastore Key uses strings and does not support byte array. the changes are done for {mainPrefix, dalcPrefix, indexerPrefix} also for {blockPrefix, indexPrefix, commitPrefix, statePrefix, responsesPrefix, validatorsPrefix}.
• some examples of storage keys after this change are:
  • blockhash: "/0/b/<block-hash>"
  • block header: "/0/i/<block-header-num>"
  • transaction indexer: "/2/tx.height/4/4/1"
  • block indexer: "/2/block_events/block.height/10"

review can follow this path:

• start with node.go
• which leads to 1) main storage (store.go), 2) dalc (files under da/ package), 3) indexer storage (block indexer: state/indexer/block/kv/kv.go and tx indexer: state/txindex/kv/kv.go)
• that's it, rest of the files are minor changes

[codecov-commenter]

Codecov Report

Merging #665 (fd1864f) into main (de83cbc) will decrease coverage by 0.42%.
The diff coverage is 76.81%.

@@ Coverage Diff @@## main #665 +/- ##
==========================================
- Coverage 55.49% 55.06% -0.43% 
==========================================
Files 50 48 -2 Lines 10353 10206 -147 ==========================================
- Hits 5745 5620 -125 + Misses 3739 3724 -15 + Partials 869 862 -7 

Impacted Files	Coverage Δ
mempool/cache.go	84.21% <ø> (ø)
mempool/clist/clist.go	75.00% <ø> (ø)
mempool/mempool.go	52.77% <ø> (ø)
state/txindex/indexer_service.go	62.96% <ø> (ø)
da/celestia/mock/server.go	49.68% <40.00%> (-0.64%)	⬇️
state/indexer/block/kv/kv.go	63.08% <68.08%> (+4.19%)	⬆️
state/txindex/kv/kv.go	64.56% <72.41%> (-2.11%)	⬇️
node/node.go	60.43% <76.47%> (-0.28%)	⬇️
da/mock/mock.go	73.75% <76.92%> (-5.80%)	⬇️
store/store.go	61.39% <84.84%> (-2.36%)	⬇️
... and 10 more

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[tzdybal]

This looks really good! But I still have some questions and comments:

1. We probably should use one of interfaces defined in go-datastore, instead of concrete go-ds-badger3 type in most places. For example celestia-node is using ds.Batching instead of ds.Datastore.
2. I don't get the difference between Batching and TxnDatastore / Batch and Txn - probably we should investigate this a bit more.
3. I think that we should return query.Results to avoid instantiating all the result objects at once.

[nashqueue]

The changes look great. Most of my comments are nits and optional. Giving me the path to review helped a lot in understanding the bigger picture. Thank you :)

[nashqueue]

LGTM

[tzdybal]

LGTM 🎉