feat(plugins): Added message read/update methods to the Channel API. (#6650)

This PR adds methods to read and update messages in a channel. Specifically, it adds:
 - message_snapshot
 - last_message
 - replace_message/replace_message_at
 - clear_messages
 - find_message_by_id
 - has_messages
 - count_messages


Reviewed-by: Mm2PL <mm2pl+gh@kotmisia.pl>

src/messages/LimitedQueue.hpp

@@ -56,6 +56,14 @@ public:
         return this->buffer_.empty();
     }
 
+    /// Number of items in this container
+    [[nodiscard]] size_t size() const
+    {
+        std::shared_lock lock(this->mutex_);
+
+        return this->buffer_.size();
+    }
+
     /// Value Accessors
     // Copies of values are returned so that references aren't invalidated
 
@@ -335,6 +343,18 @@ public:
         };
     }
 
+    template <typename U>
+    [[nodiscard]] std::vector<U> lastNBy(size_t nItems, auto &&cb) const
+    {
+        std::shared_lock lock(this->mutex_);
+        std::vector<U> vec;
+        std::transform(
+            this->buffer_.end() - std::min(nItems, this->buffer_.size()),
+            this->buffer_.end(), std::back_inserter(vec),
+            std::forward<decltype(cb)>(cb));
+        return vec;
+    }
+
     [[nodiscard]] std::vector<T> firstN(size_t nItems) const
     {
         std::shared_lock lock(this->mutex_);