Add ctor and edit few functions

mvcc.py

-import storage
+import storage as strg
 import time
 
 class MVCC :
+    def __init__(self) :
+        return
+
     def getTimestampNow(self) :
         return time.time()
 
-    def setTimestampNow(self, key, timestamp, storage = Storage) :
+    def setTimestampNow(self, key, timestamp, storage : strg) :
         tempTimestamp = timestamp
         storage.setdata[key]["timestamp"] = tempTimestamp
 
-    def read(self, key, storage = Storage) :
+    def read(self, key, storage : strg) :
         return storage.setdata[key]["value"]
     
-    def write(self, key, value, storage = Storage) :
+    def write(self, key, value, storage : strg) :
         tempTimestamp = self.getTimestampNow()
         if (storage.setdata[key]["timestamp"] > tempTimestamp) :
-            # rollback transaction and reject operation
+            # rollback transaction
+            
+            # reject operation
+            return False
         else :
             storage.setdata[key]["value"] = value
-            self.setTimestampNow(key, tempTimestamp, storage)
\ No newline at end of file
+            self.setTimestampNow(key, tempTimestamp, storage)
+            return True
\ No newline at end of file