Update CakeML CAmkES utils for style and CakeML changes

- Make derive_eval_thm work with changes to how ml_progLib
represents code thms and environments.
- Rename camkesUtils to camkesUtilsLib, to better comply with
HOL naming conventions.
- It is bizarre to first declare a function in the global
namespace, then declare an alias of said function inside
the module that the lib defines. Move the function definition
into the local namespace instead.