fix: pass XML_PARSE_UNZIP for SAX file parsing on libxml2 >= 2.14

libxml2 2.15.0 removed the automatic enabling of XML_PARSE_UNZIP in
xmlCreateFileParserCtxt, so compressed file parsing silently fails
unless the caller explicitly requests decompression.

Use xmlCreateURLParserCtxt with XML_PARSE_UNZIP on libxml2 >= 2.14
(when the flag was introduced). On older versions, fall back to
xmlCreateFileParserCtxt which auto-decompresses.

This also removes the Windows-specific test workaround for the same
issue.

Author: flavorjones

ext/nokogiri/xml_sax_parser_context.c

@@ -116,7 +116,11 @@ noko_xml_sax_parser_context_s_native_file(VALUE rb_class, VALUE rb_path, VALUE r
     rb_raise(rb_eTypeError, "argument must be an Encoding object");
   }
 
+#if LIBXML_VERSION >= 21400
+  xmlParserCtxtPtr c_context = xmlCreateURLParserCtxt(StringValueCStr(rb_path), XML_PARSE_UNZIP);
+#else
   xmlParserCtxtPtr c_context = xmlCreateFileParserCtxt(StringValueCStr(rb_path));
+#endif
   if (!c_context) {
     rb_raise(rb_eRuntimeError, "failed to create xml sax parser context");
   }

test/xml/sax/test_parser.rb

@@ -77,7 +77,6 @@ class TestCase
 
           it "parses a compressed file" do
             skip("libxml2 legacy support") unless Nokogiri.uses_libxml? && Nokogiri::LIBXML_ZLIB_ENABLED
-            skip("TODO: windows libxml 2.15.1 system libraries have ZLIB_ENABLED but it's really not") if Nokogiri::VersionInfo.instance.windows? && Nokogiri::VersionInfo.instance.libxml2_using_system?
 
             filename = XML_FILE + ".gz"
             parser.parse_file(filename)