Improve DevEx on reporting errors inside the compiler.

[reese]

Right now, reporting errors inside the compiler is really difficult, since I haven't taken the time to properly add spans inside of the parser and the file name isn't tracked inside of the type-checking stage.

There are a few things that would help here:

• Investigate thiserror as a more ergonomic way of reporting Error enums.
• Track error spans for parser errors and handle error cases inside of the LALRPop file. Alternatively, consider a hand-rolled lexer/parser for more effective error messages if that becomes a huge hassle.
• Maintain file name state during the whole compilation pipeline to pass to the codespan reporter.