Fixed ROSCONSOLE_FORMAT with microseconds

[peci1]

Currently, using the %f modifier for microseconds in ROSCONSOLE_FORMAT only works for C++ nodes. Python nodes do not interpret it:

$ export ROSCONSOLE_FORMAT='[${severity}] [${time:%d/%m/%Y %T.%f}] [${node}]: ${message}'

$ rosrun joint_state_publisher_gui joint_state_publisher_gui  # Python node
[INFO] [20/02/2024 15:19:57.%f, 0.000000] [/joint_state_publisher_gui]: Centering

$ rosrun tf2_ros static_transform_publisher 0 0 0 0 0 0 a b  # C++ node
[ INFO] [20/02/2024 14:41:05.796267] [/static_transform_publisher_1708440065774087215]: Spinning until killed publishing a to b

That is because the Python part calls time.strftime(), which uses the integer seconds. If, on the other hand, datetime is used, it uses a fractional seconds representation and is this capable of printing the microseconds.

This PR fixes the issue by switching to datetime objects. It also updates the unit test to test the feature.

[peci1]

This PR is similar to https://github.com/ros/ros_comm/pull/2367 but chose the other mentioned approach by using datetime. This PR also fixes both places where time strings can appear. Moreover, this PR adds a unit test.

[rafa-martin]

I think they will merge this feature...

[peci1]

@rafa-martin Thanks for stopping by. Would you be able to review this PR? In the low maintenance mode Noetic has, non-maintainer reviews are almost a requirement to get things moving.

[peci1]

Thanks!