--[BUGFIX] Minor bugfixes

[jturner65]

Motivation and Context

This PR fixes a few minor bugs and updates various comments.
Bugfixes :

• When saving a Managed File-based Object (such as a SceneInstanceAttributes JSON file) and not wishing to overwrite an existing copy, Habitat sim generates a numbered suffix (copy xxxx) where xxxx will be an integer sequence starting at 0000 and incrementing for each copy saved. Currently on main branch, if such a copy is then loaded in a subsequent execution and then another copy is saved, and 2nd 'copy 0000' string is appended to the name. This PR fixes this, and instead properly increments the existing copy count in the name.
• AttributesConfigsTest and AttributesManagersTest are modified to use the correct TEST_ASSETS test directory macro for file IO.
• Unnecessary 'using' statements are also removed from various metadata managers.

Local C++ and python tests pass

How Has This Been Tested

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (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 change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes.
• All new and existing tests passed.

[0mdc]

LGTM!