Feat: Add support to Action Text enabled content

Improved the `extract_content` method to correctly process Action Text. When `message` model uses `has_rich_text :content`, `message.content` becomes `ActionText:RichText`, returning HTML tags unintentionally. Adjustments ensure only the desired content is extracted.

Author: chagel

lib/ruby_llm/active_record/acts_as.rb

@@ -353,9 +353,15 @@ def extract_tool_call_id
       end
 
       def extract_content
-        return content unless respond_to?(:attachments) && attachments.attached?
+        text_content = if content.respond_to?(:to_plain_text)
+                         content.to_plain_text
+                       else
+                         content.to_s
+                       end
 
-        RubyLLM::Content.new(content).tap do |content_obj|
+        return text_content unless respond_to?(:attachments) && attachments.attached?
+
+        RubyLLM::Content.new(text_content).tap do |content_obj|
           @_tempfiles = []
 
           attachments.each do |attachment|