fix: Net::HTTP instrumentation no-op on untraced context

Update Net::HTTP instrumentation to no-op on HTTP requests within untraced
contexts. Prevents the logging of "called finish on an ended Span" messages.

Example scenario:

The Resque instrumentation can be configured to call
`OpenTelemetry::SDK::TraceProvider#force_flush` at the end of each job. That
causes the batch span processor to immediately send everything it has to the
OTLP exporter. The exporter then marks the HTTP request used to send the data
to the APM server as "untraced", by adding an `untraced` key to the context and
setting it to `true`. Before this commit, the `Net::HTTP` instrumentation did
not check for the `untraced` flag. So it would try set attributes and call
`finish` on a span that was not recording, creating one "called finish on an
ended Span" log entry for each batch of exported spans. On a large application,
that results in millions of those log entries per minute.

instrumentation/net_http/lib/opentelemetry/instrumentation/net/http/patches/instrumentation.rb

@@ -86,12 +86,20 @@ def tracer
             end
 
             def untraced?
+              untraced_context? || untraced_host?
+            end
+
+            def untraced_host?
               return true if Net::HTTP::Instrumentation.instance.config[:untraced_hosts]&.any? do |host|
                 host.is_a?(Regexp) ? host.match?(@address) : host == @address
               end
 
               false
             end
+
+            def untraced_context?
+              OpenTelemetry::Common::Utilities.untraced?
+            end
           end
         end
       end

instrumentation/net_http/test/opentelemetry/instrumentation/net/http/instrumentation_test.rb

@@ -178,6 +178,45 @@
         _(span.attributes['net.peer.port']).must_equal(80)
       end
     end
+
+    describe 'untraced context' do
+      let(:tracer_stub) { Object.new }
+      let(:expect_in_span_not_to_be_called) do
+        # Calling `tracer.in_span` within an untraced context causes the logging of "called
+        # finish on an ended Span" messages. To avoid log noise, the instrumentation must
+        # no-op (i.e., not call `tracer.in_span`) when the context is untraced.
+        def tracer_stub.in_span(...)
+          raise 'tracer.in_span should not have been called'
+        end
+      end
+
+      it 'no-ops on #request' do
+        expect_in_span_not_to_be_called
+
+        instrumentation.stub :tracer, tracer_stub do
+          OpenTelemetry::Common::Utilities.untraced do
+            Net::HTTP.get('example.com', '/body')
+          end
+        end
+
+        _(exporter.finished_spans.size).must_equal 0
+      end
+
+      it 'no-ops on #connect' do
+        expect_in_span_not_to_be_called
+
+        instrumentation.stub :tracer, tracer_stub do
+          OpenTelemetry::Common::Utilities.untraced do
+            uri = URI.parse('http://example.com/body')
+            http = Net::HTTP.new(uri.host, uri.port)
+            http.send(:connect)
+            http.send(:do_finish)
+          end
+        end
+
+        _(exporter.finished_spans.size).must_equal 0
+      end
+    end
   end
 
   describe '#connect' do