refactor bmi adapters into their own library

[hellkite500]

[Short description explaining the high-level reason for the pull request]

Changes

• Refactor the bmi adapter code into its own ngen_bmi library
• Refactor test code/organization for bmi adapters

Testing

1. All tests refactored and running locally

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️

Target Environment support

• Linux
• MacOS

[hellkite500]

Ugh...looks like I'll have to a little more work on the build refactors (not sure why I didn't run into it locally, but I'll get this cleaned up soon)

[hellkite500]

Looks like the runners are happy now...If no other changes are needed, I'll rebase my last commit and get this ready to merge. If there are some additional changes anyone thinks are required, I'll clean up with those changes.