Refactoring for better testability

[mstade]

Description

With #30 we gained some initial scaffolding for tests, and with that we'll start increasing the test coverage of this project. To that end, this PR aims to refactor ez-build to make it more testable, and ideally easier to implement new functionality as well. Additionally, integration with code coverage tooling is another explicit goal of this work.

Motivation and Context

While #30 gave us a good start, it didn't include code coverage, and also highlighted that some parts (the main routine, for instance) was muddied by mixing too many concerns.

How Was This Tested?

Additional tests are included, to increase coverage, and instrumented building is enabled for the test script as well, to ensure we can get accurate code coverage reports on every build.

Types of changes

• [x] 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:

• [x] My change follows the style of this project
• [ ] My change requires a change to the documentation
• [ ] I have updated the documentation accordingly
• [x] I have read the contribution guidelines
• [x] I have added tests to cover my changes
• [x] All new and existing tests passed

[codecov-io]

Current coverage is 78.63% (diff: 91.17%)

No coverage report found for master at e73ea49.

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[Poetro]

:+1: