Update base for Update on "[3/N] Add update function in backend interface"

Add update function in backend interface class.

Next step, will add update API in the method and then module

Differential Revision: [D75919242](https://our.internmc.facebook.com/intern/diff/D75919242/)

[ghstack-poisoned]

Author: cccclai

runtime/core/span.h

@@ -55,6 +55,9 @@ class Span final {
   template <size_t N>
   /* implicit */ constexpr Span(T (&Arr)[N]) : data_(Arr), length_(N) {}
 
+  /// Construct a Span from a single element reference.
+  /* implicit */ constexpr Span(T& single_element) : data_(&single_element), length_(1) {}
+
   /// @returns a pointer to the start of the underlying element buffer.
   iterator begin() const noexcept {
     return data_;