fix: SAX::ParserContext keeps a reference to the input (#3395)

**What problem is this PR intended to solve?**

I saw a failure in CI at
https://github.com/sparklemotion/nokogiri/actions/runs/12529532790/job/34945362057?pr=3393

```
  1) Error:
Nokogiri::HTML4::SAX::ParserContext::constructor::encoding::.io#test_0001_supports passing encoding name:
NotImplementedError: method `read' called on terminated object (0x0000005520809790)
    test/html4/sax/test_parser_context.rb:60:in `parse_with'
    test/html4/sax/test_parser_context.rb:60:in `block (5 levels) in <module:SAX>'
```

So now the class keeps a reference to the input object to prevent it
from being GCed before we parse it.


**Have you included adequate test coverage?**

Yes.


**Does this change affect the behavior of either the C or the Java
implementations?**

N/A

ext/nokogiri/xml_sax_parser_context.c

@@ -102,7 +102,10 @@ noko_xml_sax_parser_context_s_native_io(VALUE rb_class, VALUE rb_io, VALUE rb_en
     c_context->sax = NULL;
   }
 
-  return noko_xml_sax_parser_context_wrap(rb_class, c_context);
+  VALUE rb_context = noko_xml_sax_parser_context_wrap(rb_class, c_context);
+  rb_iv_set(rb_context, "@input", rb_io);
+
+  return rb_context;
 }
 
 /* :nodoc: */
@@ -154,7 +157,10 @@ noko_xml_sax_parser_context_s_native_memory(VALUE rb_class, VALUE rb_input, VALU
     c_context->sax = NULL;
   }
 
-  return noko_xml_sax_parser_context_wrap(rb_class, c_context);
+  VALUE rb_context = noko_xml_sax_parser_context_wrap(rb_class, c_context);
+  rb_iv_set(rb_context, "@input", rb_input);
+
+  return rb_context;
 }
 
 /*

test/test_memory_usage.rb

@@ -313,5 +313,29 @@ def start_element(name, attrs = [])
         # Expected error. This comment makes rubocop happy.
       end
     end
+
+    it "XML::SAX::ParserContext.io holds a reference to IO input" do
+      content = File.read(XML_ATOM_FILE)
+
+      memwatch(__method__) do
+        pc = Nokogiri::XML::SAX::ParserContext.io(StringIO.new(content), "ISO-8859-1")
+        parser = Nokogiri::XML::SAX::Parser.new(Nokogiri::SAX::TestCase::Doc.new)
+        GC.stress
+        pc.parse_with(parser)
+
+        assert_equal(472, parser.document.data.length)
+      end
+    end
+
+    it "XML::SAX::ParserContext.memory holds a reference to string input" do
+      memwatch(__method__) do
+        pc = Nokogiri::XML::SAX::ParserContext.memory(File.read(XML_ATOM_FILE), "ISO-8859-1")
+        parser = Nokogiri::XML::SAX::Parser.new(Nokogiri::SAX::TestCase::Doc.new)
+        GC.stress
+        pc.parse_with(parser)
+
+        assert_equal(472, parser.document.data.length)
+      end
+    end
   end if ENV["NOKOGIRI_MEMORY_SUITE"] && Nokogiri.uses_libxml?
 end