No need to deserialize the message via hz and bw unless necessary

[fujitatomoya]

Description

hz and bw verbs basically calculate the frequency and bandwidth for the messages on subscription.
basically it does not have to deserialize the message every time unless it needs to filter out the messages for the calculation.

for example, ros2 topic hz --filter xxx.

ros2cli/ros2topic/ros2topic/verb/hz.py

Lines 70 to 73 in f5e5a79

	parser.add_argument(
	'--filter',
	dest='filter_expr', default=None,
	help='only measure messages matching the specified Python expression', metavar='EXPR')

instead, it should receive the serialized messages and calculate the frequency and bandwidth for more performance especially large data message such as images.

Implementation Consideration

For doing this, we need to develop GenericSubscription in rclpy to receive the serialized message in the user callback with Node.create_generic_subscription just like rclcpp does.

https://github.com/ros2/rclcpp/blob/rolling/rclcpp/include/rclcpp/node.hpp#L348-L374

and then call those APIs in ros2topic if it dose not need to receive the deserialized messages.