Allow functions for GetNonNull and GetOptional to work when const.

src/Memory/BorrowedPtr.hpp

@@ -16,7 +16,7 @@ namespace Arbutils::Memory {
         inline constexpr const T* GetUnsafe() const noexcept { return _ptr; }
         inline constexpr bool IsNull() const noexcept { return _ptr == nullptr; }
 
-        inline NonNullBorrowedPtr<T> GetNonNull(){
+        inline NonNullBorrowedPtr<T> GetNonNull() const {
             return NonNullBorrowedPtr<T>(_ptr);
         }
 

src/Memory/NonNullBorrowedPtr.hpp

@@ -18,7 +18,7 @@ namespace Arbutils::Memory {
         inline constexpr T* GetUnsafe() noexcept { return _ptr; }
         inline constexpr const T* GetUnsafe() const noexcept { return _ptr; }
 
-        inline BorrowedPtr<T> GetOptional(){
+        inline BorrowedPtr<T> GetOptional() const {
             return BorrowedPtr<T>(_ptr);
         }