Add compile-time interface satisfaction checks (xj)

Add var _ Interface assertions to verify implementations at compile
time:

- internal/rpn/variables.go: assert *Variables against
  VariableReader, VariableWriter, VariablePersistence, and
  VariableStore
- internal/repl/handlers.go: assert *BuiltInCommandHandler,
  *RPNHandler, *PercentageHandler, and *ErrorHandler against
  CommandHandler (BaseHandler intentionally excluded as it lacks a
  Handle method and is only meant for embedding)
- internal/repl/completer.go: assert *AutoCompleteAdapter against
  readline.AutoCompleter (adds readline import)

Note: internal/rpn/constants.go already had assertions in place.

0 files changed, 0 insertions, 0 deletions