- kvdb
	- Fix path in Last when doing `setNew`
	- Only close if db != nil, and after closing, always set db to nil
		- This will avoid a panic in the case where the db is closed but
		  there's an error soon after, and a future call tries to close
		  again.  This is because pebble.Close() will panic if the db is
		  already closed.
	- Avoid calling pebble methods when a the Storage interface already
	  implements that method (like Close).
- statedb
	- In test, avoid calling KVDB method if the same method is available for
	  the StateDB (like MakeCheckpoint, CurrentBatch).
- eth
	- In *EventByBlock methods, take blockHash as input argument and use it
	  when querying the event logs.  Previously the blockHash was only taken
	  from the logs results *only if* there was any log.  This caused the
	  following issue: if there was no logs, it was not possible to know if
	  the result was from the expected block or an uncle block!  By querying
	  logs by blockHash we make sure that even if there are no logs, they
	  are from the right block.
	  	- Note that now the function can either be called with a
		  blockNum or blockHash, but not both at the same time.
- sync
	- If there's an error during call to Sync call resetState, which
	  internally resets the stateDB to avoid stale checkpoints (and a
	  corresponding invalid increase in the StateDB batchNum).
	- During a Sync, after very batch processed, make sure that the StateDB
	  currentBatch corresponds to the batchNum in the smart contract
	  log/event.

Last db view is an opened pebble db which always contains a checkpoint from the
last batch.  Methods to access this last batch are thread safe so that views of
the last checkpoint can be made anywhere and with a consistent view of the
state.

Update account.PublicKey to account.BJJ for naming consistency with the rest of the code

- Upgrade go-merkletree version to include the last changes of Pebble
that fixes the cgo issues (which should fix #453), from:
c2b05f12d7
- TxSelector
	- Remove parameter batchNum for GetL2TxSelection & GetL1L2TxSelection
	- Add checks of ToBJJ & ToEthAddr when ToIdx>255
	- Avoid getting the sender account twice to get the TokenID of a l2tx
	- Add test to check that selected L2Txs are sorted by Nonce
	- Discard L2Tx that return error at ProcessL2Txs
- executed `go mod tidy`

Load an ethereum keystore when the node is started in coordinator mode.  The
private key corresponding to the forger address must be imported into the
keystore before running the node in coordinator mode.  You can see an examples
in `cli/node/load-sk-example.sh`.

- KVDB contains the Checkpoint & Resets system
- StateDB uses KVDB and adds all the StateDB related methods

- Abstract TxProcessor from StateDB
- Upgrade to last version of go-merkletree for the key-value DB usage

Introduce a constructor parameter for the StateDB called `keep`, which tells
how many checkpoints to keep.  When doing a new checkpoint, if the number of
existing checkpoints exeeds `keep`, the oldest ones will be deleted.

Update usage of `*babyjub.PublicKey` to `babyjub.PublicKeyComp`
- when the key is not defined, internally is used `babyjub.EmptyBJJComp`, which is a `[32]byte` of zeroes of type `babyjub.PublicKeyComp`
- the API continues returning `nil` when the key is not defined

Checked with commonjs version:
c8414bd205

In statedb:
- Store all values using prefixes for keys to allow iteration
- Add methods MTGetRoot, GetAccounts

Implement debugapi, an http server with debugging endpoints:
- debugAPI.GET("sdb/batchnum", a.handleCurrentBatch)
- debugAPI.GET("sdb/mtroot", a.handleMTRoot)
- debugAPI.GET("sdb/accounts", a.handleAccounts)
- debugAPI.GET("sdb/accounts/:Idx", a.handleAccount)

* WIP: rebase

* Make nullable fields use pointers

Add StateDB compute nonces on ProcessTx L2Tx, and update StateDB for
type TypeSynchronizer, TypeTxSelector, TypeBatchBuilder

StateDB intermediate state reset when opening DB to force getting always last
Checkpoint at last BatchNum, avoiding inconsistent intermediate state.

Add linter checks to GHA & Fix code to pass lints.
The linters added are:
- whitespace: Tool for detection of leading and trailing whitespace
- gosec: Inspects source code for security problems
- gci: Gci control golang package import order and make it always deterministic
- misspell: Finds commonly misspelled English words in comments
- gomnd: An analyzer to detect magic numbers

The file utils/utils.go is excluded from the checks of gomnd, as uses magic numbers through the code

Update StateDB to new & ExitInfo struct & BatchNum
Also a small fix at txselector & log packages

- Update GHA lint.yml increasing timeout time to avoid GHA Lint errors
- Update common.BatchNum & common.Idx & common.Nonce usage in StateDB
- Add abstraction method of processTxs to StateDB
    - Which will be used by Synchronizer & BatchBuilder

Previously as the txprocessor.go methods were specific for the BatchBuilder,
the MTCreateAccount & CreateAccount and MTUpdateAccount & UpdateAccount were
also designed to be used by BatchBuilder and TxSelector depending on the
MerkleTree usage calling one kind of method or anotherone.

But now that this methods are being called directly by the StateDB (through the
methods in txprocessors.go), to allow also the methods usage from the
Synchronizer, there can not be the MT and no-MT methods separated, so this
commit unifies MTCreateAccount with CreateAccount, and MTUpdateAccount with
UpdateAccount, which internally will update the MerkleTree depending if the
specific StateDB in usage has the MerkleTree defined or not.