🔨 Define all singletons using CRTP

[zach2good]

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Describe the feature

It's a good pattern, makes it obvious whats going on, etc.

[zach2good]

https://stackoverflow.com/questions/51974670/implementing-singleton-with-crtp

[zach2good]

https://stackoverflow.com/questions/8147027/how-do-i-call-stdmake-shared-on-a-class-with-only-protected-or-private-const