Adopt `-Wextra` compiler error catching

[no-lex]

Adopting -Wextra level compiler error checking improves clarity of parts of the code, particularly in catching functions which have arguments that do not get used among other things. Doing so will help to cull some apparent complexity from the codebase and make it easier to follow.

[no-lex]

Note: The above commit is relevant because unused parameters are one of the warnings spammed by -Wextra (before adopting the flag officially, it'd be good to not make the build look like crap)