Use `DuplicateRecordFields`, `NoFieldSelectors`, and `OverloadedRecordDot`

[jorisdral]

In the Haskell Unfolder episode on records, a strong case is made for using the language exensions DuplicateRecordFields, NoFieldSelectors, and OverloadedRecordDot. We use record syntax quite a bit in this repository, and we can make all that syntax more succinct by enabling these language extensions globally.