Add base structure and library stuff from last year

src/main/scala/de.qwertyuiop.aoc/lib/extensions.scala

@@ -0,0 +1,23 @@
+package de.qwertyuiop.aoc.lib
+
+/* for splitting input with separator lines */
+extension [A](input: List[A])(using CanEqual[A,A])
+  def split(separator: A, keepSeparator: Boolean = false): LazyList[List[A]] =
+    input.span(_ != separator) match
+        case (Nil, Nil)              => LazyList()
+        case (h,   Nil)              => LazyList(h)
+        case (h,   tail @ (_ :: t)) =>
+          h #:: (if keepSeparator then tail else t).split(separator)
+
+
+/* Using -Yexplicit-nulls isn't really ready for use with the java standard
+ * library. e.g. String doesn't have `@NotNull` annotations for its methods
+ */
+extension (s: String)
+  def splitOnce(regex: String): Option[(String, String)] =
+    s.split(regex, 2) match
+      case Array(a, b) => Some((a.nn, b.nn))
+      case _ => None
+
+extension [K,V,W](map: Map[K,V])
+  def mapValuesS(f: V => W): Map[K, W] = map.view.mapValues(f).toMap