Apply Fourmolu to `plutus-tx-plugin` package

[Unisay]

This task is to apply fourmolu configuration specified by the fourmolu.yaml in the project root to the plutus-tx-plugin subfolder.

It is ok to skip modules initially by adding the FOURMOLU_DISABLE annotation and re-format them later in the opportunistic manner. Please check the official doc on how to use "magic comments".

You can follow these steps:

$ cd plutus-tx-plugin
$ find src -name "*.hs" -exec fourmolu -i {} \; # reformats all *.hs under the `src` folder with fourmolu
$ find src -name "*.hs" -exec stylish-haskell -i {} \; # applies `stylish-haskell` on top of the fourmolu

Then scrutinize the diff manually disabling fourmolu formatting where appropriate using the "magic comments".