Add missing is_empty methods

asl/containers/buffer.hpp

@@ -273,6 +273,8 @@ public:
         return decode_size(load_size_encoded());
     }
 
+    [[nodiscard]] constexpr bool is_empty() const { return size() == 0; }
+
     [[nodiscard]] constexpr isize_t capacity() const
     {
         if constexpr (kInlineCapacity == 0)

asl/containers/hash_map.hpp

@@ -96,6 +96,8 @@ public:
 
     using Base::size;
 
+    using Base::is_empty;
+
     using Base::remove;
 
     using Base::contains;

asl/containers/hash_set.hpp

@@ -386,6 +386,8 @@ public:
 
     [[nodiscard]] constexpr isize_t size() const { return m_size; }
 
+    [[nodiscard]] constexpr bool is_empty() const { return m_size == 0; }
+
     template<typename... Args>
     void insert(Args&&... args)
         requires constructible_from<T, Args&&...>

asl/strings/string.hpp

@@ -45,6 +45,9 @@ public:
     constexpr string& operator=(string&&) = default;
 
     [[nodiscard]] constexpr isize_t size() const { return m_buffer.size(); }
+
+    [[nodiscard]] constexpr bool is_empty() const { return m_buffer.is_empty(); }
+
     [[nodiscard]] constexpr const char* data() const { return m_buffer.data(); }
 
     // NOLINTNEXTLINE(*explicit*)