✅ Make FakeServer more robust against disconnect

When the client disconnects without a `LOGOUT`, that shouldn't cause a
secondary error in the test output.  Most of the time, it's just a
distraction.  In some cases, the test is intentionally triggering a bad
disconnect, and the server's failure could break the test.

Author: nevans

test/net/imap/fake_server/command_reader.rb

@@ -21,6 +21,7 @@ def get_command
         $2 or socket.print "+ Continue\r\n"
         buf << socket.read(Integer($1))
       end
+      throw :eof if buf.empty?
       @last_command = parse(buf)
     end
 

test/net/imap/fake_server/connection.rb

@@ -23,7 +23,9 @@ def unsolicited(...) writer.untagged(...) end
 
     def run
       writer.greeting
-      router << reader.get_command until state.logout?
+      catch(:eof) do
+        router << reader.get_command until state.logout?
+      end
     ensure
       close
     end

test/net/imap/fake_server/test_helper.rb

@@ -14,7 +14,11 @@ def run_fake_server_in_thread(ignore_io_error: false, timeout: 10, **opts)
       end
       yield server
     ensure
-      server&.shutdown
+      begin
+        server&.shutdown
+      rescue IOError
+        raise unless ignore_io_error
+      end
     end
   end