This mode reduces the size of test cases that encounter conversion
errors or produce incorrect output. The logic developed slowly over the
past three years. It is in a state that I find useful when fielding bug
reports, but has some room for improvement in terms of constraints and
filtering.

- use iverilog's -gstrict-expr-width throughout test suite
- add warnings for excess bits or padding zeroes in number literals
- add new --oversized-numbers parameter to retain support for unsized
  numbers wider than 32 bits
- localized use of oversized numbers to new truncate test suite which
  verifies the behavior of both modes, and compares against the known
  behavior of iverilog

- add unified frontend configuration record to make adding future
  options easier
- use ExceptT throughout, rather than using runExceptT at internal
  boundaries

- warnings were skipped because verbose about was technically not empty
- add test suite for these warnings in both modes

- error for unbound module instance interface ports
- warning for converting an interface alone
- warning for converting a package alone
- update terminology for modules removed by interface conversion

- NestTF refactored to cover all package items
- fixed issue where type traverse skipped typedefs