Fix warnings about non-virtual destructors for non-BMI classes with virtual methods

[PhilMiller]

We want to build warning-clean, and -Wnon-virtual-dtor can signal some serious potential errors. This PR fixes internal cases that trigger the warning.

Changes

• Formulation_Manager and HydrofabricSubsetter: remove virtual marking on member functions, since the classes don't have descendants that need virtual dispatch
• geojson::FeatureVisitor: add virtual destructor

Testing

1. CI

Notes

• BMI module class change will come in a separate PR, that changes both our copies and external git submodules together

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 ➡️