p2p: add network simulation framework (#14982)

This commit introduces a network simulation framework which
can be used to run simulated networks of devp2p nodes. The
intention is to use this for testing protocols, performing
benchmarks and visualising emergent network behaviour.

p2p/server_test.go

@@ -435,7 +435,7 @@ func TestServerSetupConn(t *testing.T) {
 			}
 		}
 		p1, _ := net.Pipe()
-		srv.setupConn(p1, test.flags, test.dialDest)
+		srv.SetupConn(p1, test.flags, test.dialDest)
 		if !reflect.DeepEqual(test.tt.closeErr, test.wantCloseErr) {
 			t.Errorf("test %d: close error mismatch: got %q, want %q", i, test.tt.closeErr, test.wantCloseErr)
 		}