ethdb: more accurate batch size calculation (ethereum#23790)

This PR also counts the size of the key when calculating the size of a db batch

ethdb/leveldb/leveldb.go

@@ -455,7 +455,7 @@ type batch struct {
 // Put inserts the given value into the batch for later committing.
 func (b *batch) Put(key, value []byte) error {
 	b.b.Put(key, value)
-	b.size += len(value)
+	b.size += len(key) + len(value)
 	return nil
 }
 

ethdb/memorydb/memorydb.go

@@ -204,7 +204,7 @@ type batch struct {
 // Put inserts the given value into the batch for later committing.
 func (b *batch) Put(key, value []byte) error {
 	b.writes = append(b.writes, keyvalue{common.CopyBytes(key), common.CopyBytes(value), false})
-	b.size += len(value)
+	b.size += len(key) + len(value)
 	return nil
 }