ENH: include save_tree_to_path from #54

[ZLLentz]

Description

Include save_tree_item_to_path, a companion to get_tree_from_path that takes a fully constructed behavior tree item and saves it to a json file. It is intended that any tree serialized this way will be usable by get_tree_from_path.

Motivation and Context

I had to google apischema's API to serialize my behavior tree and I thought I shouldn't have to do that.

How Has This Been Tested?

Interactively and added a unit test.

Where Has This Been Documented?

I added a pre-release documentation entry.

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]

The only thing here to nitpick is the lack of parameter types and explanations in the docstring (As per numpy docstring conventions). I imagine the function parameters are pretty self explanatory here, but you never know. (maybe also for future auto-generated docs)

The docstrings etc here need a lot more work before we get there anyway.

[tangkong]

I usually invoke serialize the same way I do deserialize, to be explicit. I think apischema does this conversion for you if you don't provide it, but I have trust issues:

ser = serialize(BehaviourTreeItem, tree_item)

[ZLLentz]

I'm not sure I quickly understand what tree_item is in this case.

[joshc-slac]

Very valuable. We can cut issue to capture notion of extending this to perform a "snapshot" ability - serialize the tree at a given state, with Status's of given nodes captured as well. This will deliver that ability