- reduces the number of cast functions which are generated
- adjust package_function_cast to preserve cast converage
- fix issue where cast functions would be generated before localparam
  substitution within a procedure

This reverts commit 51f2d2bb.

- added type class for looking up elements in scoped conversions

- support casts of generate scoped expressions
- support casts to sizes involving genvars

- number literals are parsed rather than stored as strings
- fix array query functions used on non-trivial number literals
- more efficient expression simplification recursion
- expanded constant folding scenarios

- elaborated literals larger than 32 bits are given an explicit size
- constant folding no longer encodes illegal negative numbers