BUG: check both dataclass and EntryItem in tree view in canFetchMore

[tangkong]

Description

Previously RootTree.canFetchMore would check the dataclass members to determine if filling was necessary. This works within the context of a single page, but if we open the a detailed page from the tree-view the dataclass may be filled without the EntryItem getting filled.

Now that RootTree.canFetchMore checks both the dataclass and the EntryItem, this desync can be avoided

Motivation and Context

Closes #113

How Has This Been Tested?

Interactively

Where Has This Been Documented?

This PR, pre-release notes

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