Add scalafmt formatter + build

.scalafmt.conf

+# https://diamantidis.github.io/2020/05/17/ci-with-github-actions-for-scala-project
+version = "3.3.0"
+
+runner.dialect = scala3
+rewrite.scala3.convertToNewSyntax = true
+
+maxColumn = 120
+
+indent.main = 4
+indent.callSite = 4
+
+project.git = true

build.sbt

+lazy val root = (project in file("."))
+  .settings(
+    name := "prog-2",
+    scalaVersion := "3.1.0"
+  )

project/build.properties

+sbt.version=1.5.4