Print hook argument values on crash

[Baltoli]

This PR implements hook argument printing for all hook arguments that aren't K terms (i.e. numeric and string arguments). Combined with #599, this means that when a hook crashes in the LLVM backend, you can see precisely which hook it was, as well as the actual argument values that caused the crash. This should save a lot of debugging and investigating time.

To implement the change without adding additional dependencies to the runtime components of the backend, this PR contains a tiny implementation of a std::format lookalike that we should aim to drop whenever C++20 is mainstream. We now just pull in fmt as it's not an onerous dependency to use.

[dwightguth]

I left a couple comments. Also, the string library already depends on the int and float libraries; I don't think we probably need to create a whole separate library just for the conversion functions, which ought to significantly simplify this diff.

[dwightguth]

You reused the existing code for converting floats to strings, but not the existing code for converting ints to strings. I would rather we reuse the code that already exists as it has been thoroughly tested.

[Baltoli]

No problem; will address this in the appropriate way depending on your opinion on the dependency graph question below.

[Baltoli]

Also, the string library already depends on the int and float libraries; I don't think we probably need to create a whole separate library just for the conversion functions, which ought to significantly simplify this diff.

The dependency graph in this PR currently looks like this:

If we were to pull numeric_strings back into the strings library, we'd end up with a circular dependency, which is what I was aiming to avoid as a question of taste (really not a big deal though, as CMake is happy to link it for you, I think). Happy to use the circular version if you'd prefer that.