Integrate purger to node

- Common
	- Add `IdxNonce` type used to track nonces in accounts to invalidate
	  l2txs in the pool
- Config
	- Update coordinator config will all the new configuration parameters
	  used in the coordinator
- Coordinator
	- Introduce the `Purger` to track how often to purge and do the job when
	  needed according to a configuration.
	- Implement the methods to invalidate l2txs transactions due to l2txs
	  selection in batches.  For now these functions are not used in favour
	  of the `Purger` methods, which check ALL the l2txs in the pool.
	- Call Invalidation and Purging methods of the purger both when the
	  node is forging (in the pipeline when starting a new batch) and when
	  the node is not forging (in coordinator when being notified about a
	  new synced block)
- L2DB:
	- Implement `GetPendingUniqueFromIdxs` to get all the unique idxs from
	  pending transactions (used to get their nonces and then invalidate
	  txs)
	- Redo `CheckNonces` with a single SQL query and using `common.IdxNonce`
	  instead of `common.Account`
- StateDB:
	- Expose GetIdx to check errors when invalidating pool txs
- Synchronizer:
	- Test forged L1UserTxs processed by TxProcessor
	- Improve checks of Effective values
- TxSelector:
	- Expose the internal LocalStateDB in order to check account nonces in
	  the coordinator when not forging.

db/statedb/statedb.go

@@ -303,7 +303,7 @@ func (s *StateDB) reset(batchNum common.BatchNum, closeCurrent bool) error {
 		return tracerr.Wrap(err)
 	}
 	// idx is obtained from the statedb reset
-	s.idx, err = s.getIdx()
+	s.idx, err = s.GetIdx()
 	if err != nil {
 		return tracerr.Wrap(err)
 	}

db/statedb/txprocessors.go

@@ -1118,9 +1118,9 @@ func (s *StateDB) computeEffectiveAmounts(tx *common.L1Tx) {
 	}
 }
 
-// getIdx returns the stored Idx from the localStateDB, which is the last Idx
+// GetIdx returns the stored Idx from the localStateDB, which is the last Idx
 // used for an Account in the localStateDB.
-func (s *StateDB) getIdx() (common.Idx, error) {
+func (s *StateDB) GetIdx() (common.Idx, error) {
 	idxBytes, err := s.DB().Get(keyidx)
 	if tracerr.Unwrap(err) == db.ErrNotFound {
 		return 0, nil