Fix 'value out of range' RangeDefect in block witness generation. (#2072)

* Fix 'value out of range' RangeDefect caused by large/expensive blocks/transactions during DOS period.

* Clear witness cache in AccountCache persist.

* Revert previous fix and force clear cache after processing each block.

* Revert clear cache in process block.

nimbus/db/ledger/accounts_cache.nim

@@ -694,6 +694,10 @@ proc makeMultiKeys*(ac: AccountsCache): MultiKeysRef =
     result.add(k, v.codeTouched, multiKeys(v.storageKeys))
   result.sort()
 
+  # reset the witness cache after collecting the witness data
+  # so it is clean before executing the next block
+  ac.witnessCache.clear()
+
 proc accessList*(ac: AccountsCache, address: EthAddress) {.inline.} =
   ac.savePoint.accessList.add(address)
 

stateless/multi_keys.nim

@@ -32,7 +32,7 @@ type
   MultiKeysRef* = ref MultiKeys
 
   Group* = object
-    first*, last*: int16
+    first*, last*: int
 
   BranchGroup* = object
     mask*: uint