BUG/MNT: return InvalidResult if container is malformed

[tangkong]

Description

Creates an InvalidResult that may be returned if a container is malformed. Exceptions are still raised if keys do not exist. This does change the behavior of a few methods, which used to simply skip results that couldn't be created.

This could be considered an API break.

Fixes a variety of type hinting errors along the way

Motivation and Context

#299

Also I wanted to test pcds-6.0.1 development

How Has This Been Tested?

Mostly through test suite

Where Has This Been Documented?

This PR

Pre-merge checklist

• Code works interactively
• 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

[ZLLentz]

This makes sense and I think is well-motivated.
I'm trying to be a little cautious because it is an API break on some level.
For users with well-formed databases it will behave the same at least.

[ZLLentz]

I'm on board. Not sure if you want to let this sit and percolate or not (it's an API break after all).

[tangkong]

I'll merge this as is (with extra docs context added). I'll go about making followup issues for the unresolved comments.