OCaml: Add formatting configuration

ocaml/.ocamlformat

@@ -0,0 +1,8 @@
+version = 0.27.0
+margin-check = true
+extension-indent = 4
+function-indent = 4
+type-decl-indent = 4
+let-binding-indent = 4
+indicate-nested-or-patterns = space
+indicate-multiline-delimiters = closing-on-separate-line

ocaml/justfile

@@ -11,8 +11,8 @@ test :
 format :
     dune fmt; dune promote
 
-check-format :
-    dune build fmt
+format-check fmt-ck :
+    dune fmt --preview
 
 cover :
     find . -name '*.coverage' -exec rm -v '{}' ';'