Improve compile times by 25%

[jeaye]

This drops (serial) compile times from ~980s to ~740 seconds. This is important not just for our dev experience, but because we'll ultimately be including more of these header during runtime and startup. We need them to be as light as possible. I used clang build analyzer for figuring out the most important things to tackle. There's a lot more which can be done (we can definitely get under 500s), but for now this PR includes:

• Replace static_object with distinct object types
• Remove magic_enum in favor of constexpr fns
• Move various CRTP templates into cpp files with explicit instantiations
• Remove fmt from headers and provide a custom string builder instead
  • fmt is still used within cpp files (for now)
• Clean up lots of includes based on all of the changes above