Increase max file unit

[dzalkind]

Description and Purpose

Minor changes that allow more file to be written/read and closes debug files at the end of a simulation. Could be helpful for when many checkpoints are written, as in #251.

The issue in #251 has not yet been reproduced, so the root cause of that issue may remain.

Type of change

What types of change is it?
Select the appropriate type(s) that describe this PR

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

TODO Items General:

• Add example/test for new feature
• Update registry
• Run testing

TODO Items API Change:

• Update docs with API change
• Run update_rosco_discons.py in Test_Cases/
• Update DISCON schema

Github issues addressed, if one exists

Examples/Testing, if applicable