Update Snapshot & Root approach to get the root always from the db,
except in the cases that the tree is a snapshot, in which the root will
be in memory.
In this way, when a snapshot is performed and the original tree gets
modifyed, the snapshot will still point to the old root. Also, the root
obtained from the db, uses also the db.ReadTx, so if the root is being
modifyied in the current tx (db.WriteTx), when getting the root it will
be return the lastest version that is in the tx but not yet in the db.
Case tree empty, AddBatch was 10.95x times faster than without AddBatch
nCPU: 4, nLeafs: 1024, hash: Poseidon, db: memory
dbgStats(hash: 2.047k, dbGet: 1, dbPut: 2.049k)
Case tree not empty w/ few leafs, AddBatch was 7.28x times faster than without AddBatch
nCPU: 4, nLeafs: 1024, hash: Poseidon, db: memory
dbgStats(hash: 2.047k, dbGet: 198, dbPut: 2.049k)
Case tree not empty w/ enough leafs, AddBatch was 5.94x times faster than without AddBatch
nCPU: 4, nLeafs: 1024, hash: Poseidon, db: memory
dbgStats(hash: 2.047k, dbGet: 1.000k, dbPut: 2.049k)
Case tree not empty, AddBatch was 9.27x times faster than without AddBatch
nCPU: 4, nLeafs: 4096, hash: Poseidon, db: memory
dbgStats(hash: 8.191k, dbGet: 1.800k, dbPut: 8.193k)
Case tree not empty & unbalanced, AddBatch was 10.67x times faster than without AddBatch
nCPU: 4, nLeafs: 4096, hash: Poseidon, db: memory
dbgStats(hash: 10.409k, dbGet: 2.668k, dbPut: 10.861k)
TestAddBatchBench: nCPU: 4, nLeafs: 50000, hash: Blake2b, db: badgerdb
Add loop: 10.10829114s
AddBatch: 732.030263ms
dbgStats(hash: 122.518k, dbGet: 1, dbPut: 122.520k)
TestDbgStats
add in loop in emptyTree dbgStats(hash: 141.721k, dbGet: 134.596k, dbPut: 161.721k)
addbatch caseEmptyTree dbgStats(hash: 24.402k, dbGet: 1, dbPut: 24.404k)
addbatch caseNotEmptyTree dbgStats(hash: 26.868k, dbGet: 2.468k, dbPut: 26.872k)
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