Adding vtkhdf

[shimwell]

Proposed changes

Just seeing if vtkhdf reading could fit into this package.

draft PR, work in progress but I want to show the idea

Types of changes

What types of changes does your code introduce to openmc2dolfinx?

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactoring
• Documentation Update (if none of the other choices apply)
• New tests

Checklist

• Unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)