Bmi_Adapter cleanup, de-template

[PhilMiller]

Templates that don't actually provide any polymorphic behavior are just a waste of compilation time and binary size. So, get rid of one.

Also, implementation inheritance (the bmi_model member) isn't very favorable in general, and even less so when the base class isn't actually providing anything

Changes

• Simplify implementation of Bmi_Adapter class to make further refactoring easier
• Move the single CRTP template-parameter-dependent shared_ptr<T> bmi_model member down to child classes
• De-template Bmi_Adapter
• Improve an error message that would have helped with an intermediate bug in my changes
• Mark copy/move constructors that shouldn't get called = delete;
• Convert member pointers 'bmi_model' to various backing types from shared_ptr to unique_ptr to clarify that they have strict exclusive ownership

Testing

Ordinary CI test suite

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 ➡️

[PhilMiller]

I think this is ready for re-review and integration. I'm done poking at the adapters for now. I'm going to try to tackle some of the rampant silly duplication in the Formulation classes next.