wikipedia: increase REXML entity expansion limit during XML parsing

Using `Datasets::Wikipedia#each` raised an `entity expansion has grown too large (RuntimeError)`.
This error occurs because the entity expansion limit in REXML is set by ruby/rexml#187,
and `Datasets::Wikipedia#each` exceeds that limit.

In Red Datasets, increasing the entity expansion limit is not a problem because we want to handle large datasets.
Therefore, we temporarily increase the limit.

```ruby
require 'datasets'

wikipedia = Datasets::Wikipedia.new
wikipedia.each do |wiki|
  pp wiki
end
```

```console
$ cd red-datasets && bundle && bundle exec ruby wiki
/home/otegami/.rbenv/versions/3.3.3/lib/ruby/gems/3.3.0/gems/rexml-3.3.4/lib/rexml/parsers/baseparser.rb:560:in `block in unnormalize': entity expansion has grown too large (RuntimeError)
```

lib/datasets/wikipedia.rb

@@ -48,11 +48,16 @@ def each(&block)
       open_data do |input|
         listener = ArticlesListener.new(block)
         parser = REXML::Parsers::StreamParser.new(input, listener)
-        parser.parse
+        with_increased_entity_expansion_text_limit do
+          parser.parse
+        end
       end
     end
 
     private
+
+    ENTITY_EXPANSION_TEXT_LIMIT = 1_342_177_280
+
     def base_name
       "#{@language}wiki-latest-#{type_in_path}.xml.bz2"
     end
@@ -80,6 +85,14 @@ def type_in_path
       end
     end
 
+    def with_increased_entity_expansion_text_limit
+      default_limit = REXML::Security.entity_expansion_text_limit
+      REXML::Security.entity_expansion_text_limit = ENTITY_EXPANSION_TEXT_LIMIT
+      yield
+    ensure
+      REXML::Security.entity_expansion_text_limit = default_limit
+    end
+
     class ArticlesListener
       include REXML::StreamListener