feat: internal state machine and test code

[ChandimaFernando]

This PR implements the logic of the inner state machine for the pdf_beamtime.
Added internal state machine functions as follows:

Initial tests for the inner and outer state transitions for an uninterrupted pick-and-place task have been completed successfully.

[maffettone]

Ideally what this PR should contain is an actual working implementation of the Inner and Outer state machines. Right now it just has the implementation of the inner state machine, but no modifications to show how it will work in practice, or tests of that ongoing.

There's no need to "disregard changes in xxx". Implement the changes that are actually needed to affect the behavior desired. And write at minimum an acceptance test (in somewhere outside of src) that will demonstrate the behavior.

That could be something that involves spinning up the containers and saying, "this simple program should produce this output in the logs". It is not quite a unit test, but it shows what you are trying to accomplish.

[maffettone]

This is looking good. Some minor edits and a question to address tomorrow to make sure we're on the same page.

Looks like black is newly failing CI/CD on python files not involved with this PR, so should not block. A maintenance PR will be needed to address either the CI/CD or the black failures.

[maffettone]

I'm still a little unsure why the InnerStateMachine needs to know about the external state? Is this just for logging?

[ChandimaFernando]

In the earlier version before separating the internal state machine from the external one, I used the external state to control internal state logic. After the separation., right now it is only used for logging.

[ChandimaFernando]

InnerStateMachine only accepts node_ as its sole argument. the external state is removed. Respective changes were made to inner_state_machine.hpp and README.md

erobs/src/pdf_beamtime/src/pdf_beamtime_server.cpp

Line 53 in e33193c

inner_state_machine_ = new InnerStateMachine(node_);

erobs/src/pdf_beamtime/src/inner_state_machine.cpp

Lines 5 to 7 in e33193c

	InnerStateMachine::InnerStateMachine(
	const rclcpp::Node::SharedPtr node)
	: node_(node)

https://github.com/maffettone/erobs/blob/19470036fe498c0d3a4e50f68608ac4b79c722f0/src/pdf_beamtime/README.md