First step towards modernizing the rt publisher (backport #210)

[mergify]

I think the rt publisher is one of the most commonly used tools in this package.
When ever I was using it I stumbled upon its "weird" API.

This PR is a first step towards modernizing the RealtimePublisher class, providing a tiny bit of comfort by adding a tryPublish method and providing some typedefs similar to the rclcpp::Publisher.

I plan to add a follow up PR where I refactor the NON_POLLING define into a template parameter.

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This is an automatic backport of pull request #210 done by Mergify.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.54%. Comparing base (c4407c8) to head (d480b1e).

Additional details and impacted files

@@            Coverage Diff             @@
##           humble     #233      +/-   ##
==========================================
+ Coverage   76.15%   76.54%   +0.39%     
==========================================
  Files           8        8              
  Lines         478      486       +8     
  Branches      183      184       +1     
==========================================
+ Hits          364      372       +8     
  Misses         77       77              
  Partials       37       37              

Flag	Coverage Δ
unittests	76.54% <100.00%> (+0.39%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
include/realtime_tools/realtime_publisher.hpp	96.82% <100.00%> (+0.46%)	⬆️

[saikishor]

LGTM