feat: add template expected<T, E>::rebind<U>

Author: X1aomu

include/zeus/expected.hpp

@@ -1194,6 +1194,9 @@ class expected
     typedef E             error_type;
     typedef unexpected<E> unexpected_type;
 
+    template<class U>
+    using rebind = expected<U, error_type>;
+
     // default constructors
 
     constexpr expected()                    = default;
@@ -2143,6 +2146,9 @@ class expected<void, E>
     typedef E             error_type;
     typedef unexpected<E> unexpected_type;
 
+    template<class U>
+    using rebind = expected<U, error_type>;
+
     constexpr expected()                    = default;
     constexpr expected(const expected &rhs) = default;
     constexpr expected(expected &&rhs)      = default;