Add fourmolu to CI and apply it to the project

.github/workflows/fourmolu.yaml

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+name: Fourmolu
+on: push
+jobs:
+  format:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: haskell-actions/run-fourmolu@v10
+        with:
+          version: "0.15.0.0"
+

fourmolu.yaml

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+# Number of spaces per indentation step
+indentation: 2
+
+# Max line length for automatic line breaking
+column-limit: none
+
+# Styling of arrows in type signatures (choices: trailing, leading, or leading-args)
+function-arrows: leading
+
+# How to place commas in multi-line lists, records, etc. (choices: leading or trailing)
+comma-style: leading
+
+# Styling of import/export lists (choices: leading, trailing, or diff-friendly)
+import-export-style: leading
+
+# Whether to full-indent or half-indent 'where' bindings past the preceding body
+indent-wheres: true
+
+# Whether to leave a space before an opening record brace
+record-brace-space: true
+
+# Number of spaces between top-level declarations
+newlines-between-decls: 1
+
+# How to print Haddock comments (choices: single-line, multi-line, or multi-line-compact)
+haddock-style: single-line
+
+# How to print module docstring
+haddock-style-module: null
+
+# Styling of let blocks (choices: auto, inline, newline, or mixed)
+let-style: inline
+
+# How to align the 'in' keyword with respect to the 'let' keyword (choices: left-align, right-align, or no-space)
+in-style: no-space
+
+# Whether to put parentheses around a single constraint (choices: auto, always, or never)
+single-constraint-parens: never
+
+# Whether to put parentheses around a single deriving class (choices: auto, always, or never)
+single-deriving-parens: always
+
+# Output Unicode syntax (choices: detect, always, or never)
+unicode: never
+
+# Give the programmer more choice on where to insert blank lines
+respectful: true
+
+# Fixity information for operators
+fixities: []
+
+# Module reexports Fourmolu should know about
+reexports: []