verilog: fix sizing of constant args for tasks/functions

verilog: fix sizing of constant args for tasks/functions

- Simplify synthetic localparams for normal calls to update their width
    - This step was inadvertently removed alongside `added_mod_children`
- Support redeclaration of constant function arguments
    - `eval_const_function` never correctly handled this, but the issue
      was not exposed in the existing tests until the recent change to
      always attempt constant function evaluation when all-const args
      are used
- Check asserts in const_arg_loop and const_func tests
- Add coverage for width mismatch error cases