Adding GC content calculations

[elder099]

Description

Please include a summary of the changes being made within your PR. Please also include relevant motivation and context.

Type of change

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• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also note any relevant details for your test configuration.
Confirmed output value of 50% GC content on benchmark data and compared to expected output (also 50%).

Checklist:

• My code adheres to the repository style guide
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing tests pass locally with my changes

[kevinlibuit]

Jesse, changes look great RE GC calc/reporting + updated tests!