Entry RemoveReason is iota based with default value being 0

Currently all const for RemovedReason are explicitly
set to avoid any breaking changes. For v3 migrating the reasons
to iota makes code readability and managing addition of more reasons
easier in the future.

Test: Validated all test cases run successfully.

bigcache.go

@@ -34,12 +34,12 @@ type RemoveReason uint32
 const (
 	_ RemoveReason = iota
 	// Expired means the key is past its LifeWindow.
-	Expired = RemoveReason(1)
+	Expired
 	// NoSpace means the key is the oldest and the cache size was at its maximum when Set was called, or the
 	// entry exceeded the maximum shard size.
-	NoSpace = RemoveReason(2)
+	NoSpace
 	// Deleted means Delete was called and this key was removed as a result.
-	Deleted = RemoveReason(3)
+	Deleted
 )
 
 // NewBigCache initialize new instance of BigCache