wip: addressing issue #56, allowing for us to determine how often we caput

[joshc-slac]

Description

This is likely not the best way to do this but I want to motivate a few things:

• chopping up tree_config.py into logical units
• adding derived base class support to our serialization schema
• ask if this type of feature should be implemented at this layer, or hidden from super users within the wrapped_action_work helper
• ask if it is not better to just change the loop frequency...
• we could also use BT style decorators... but this would still make us add a mechanism that routed tick timing to work function (via Semaphore most likely)

Motivation and Context

We don't necessarily want to spam EPICS with caput requests. This is a mechanism to do that

How Has This Been Tested?

Extended test cases to exercise this feature

Where Has This Been Documented?

Probably needs a little something

##Alternatives:
Instantiating a semaphore in ActionNode that is passed to ActionWorker to be wrapped and then using the semaphore to pass ticks which gate execution of the work function might be cleaner.

Pre-merge checklist

• Code works interactively
• Code follows the style guide
• Code contains descriptive docstrings, including context and API
• New/changed functions and methods are covered in the test suite where possible
• Test suite passes locally
• Test suite passes on GitHub Actions
• Ran docs/pre-release-notes.sh and created a pre-release documentation page
• Pre-release docs include context, functional descriptions, and contributors as appropriate

[tangkong]

I think this timer stuff probably makes the most sense living in the ActionNode, not the tree-item class. The purpose of the *Item here is to assist with serialization, and the *Node does the actual work.

We already did a bunch of work moving references away from the TreeItem into the ActionNode, it feels like a step backward to do so again.

[joshc-slac]

That's a very good point