[core] Use int64_t instead of int to keep track of fractional resources (#4959)

src/ray/raylet/scheduling_resources.cc

@@ -18,7 +18,8 @@ FractionalResourceQuantity::FractionalResourceQuantity(double resource_quantity)
   RAY_CHECK(resource_quantity >= 0) << "Resource capacity, " << resource_quantity
                                     << ", should be nonnegative.";
 
-  resource_quantity_ = static_cast<int>(resource_quantity * kResourceConversionFactor);
+  resource_quantity_ =
+      static_cast<int64_t>(resource_quantity * kResourceConversionFactor);
 }
 
 const FractionalResourceQuantity FractionalResourceQuantity::operator+(

src/ray/raylet/scheduling_resources.h

@@ -58,7 +58,7 @@ class FractionalResourceQuantity {
  private:
   /// The resource quantity represented as 1/kResourceConversionFactor-th of a
   /// unit.
-  int resource_quantity_;
+  int64_t resource_quantity_;
 };
 
 /// \class ResourceSet