Print special float values as Num.nanF64, etc

[andyferris]

Addresses part of #6709. I might need a little bit of help on this one.

My understanding of rust macros is limited - I suspect the f64_helper! and f32_helper! macros could be elided. I was trying to avoid adding a trait just for dispatching on the number printing function at the end.

I also think my usage of Expr::Num("Num.nanF64") is wrong since we aren't actually implementing these as literals - there must be another AST node type for getting something from a module?

There are a few pieces of documentation in Num.roc that could be updated to reflect these changes.

Finally, I wasn't sure if there was any runtime (zig) code for printing numbers as strings that we also want to consider? (Sorry, my understanding of the system as a whole is limited at this stage).

[andyferris]

OK I've managed to get this running well locally. I am seeing a test failure for cli_run::expects_dev_and_test but I don't see the relationship.

[lukewilliamboswell]

I rebased on main and can't reproduce the test failure. Let's see what CI has to say 🤷‍♂️