refactor: units submodule

[maxwellmattryan]

Summary

Please summarize your changes, describing what they are and why they were made.

This PR takes existing code from the old lib/units.ts file and refactors it into a utils submodule. It only deals with re-organizing code; NOT refactoring logic.

Changelog

- Refactor existing code into utils submodule
- Remove types file for `utils`

Relevant Issues

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Closes #3973

Testing

Platforms

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• Desktop
  • MacOS
  • Linux
  • Windows
• Mobile
  • iOS
  • Android

Instructions

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Tested general app functionality, particularly around the send flow.

Checklist

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• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or modified tests that prove my changes work as intended
• I have verified that new and existing unit tests pass locally with my changes
• I have verified that my latest changes pass CI workflows for testing and linting
• I have made corresponding changes to the documentation

[jeeanribeiro]

LGTM 😄