Add unrelated test

I wanted to get the test in anyway and this will hopefully get the CI unstuck.

Author: odersky

tests/pos/matrixOps.scala

@@ -0,0 +1,17 @@
+object Test with
+
+  type Matrix = Array[Array[Double]]
+  type Vector = Array[Double]
+
+  given (m: Matrix)
+    def nRows = m.length
+    def nCols = m(0).length
+    def row(i: Int): Vector = m(i)
+    def col(j: Int): Vector = Array.tabulate(m.length)(i => m(i)(j))
+
+  def pairwise(m: Matrix) =
+    for
+      i <- 0 until m.nRows
+      j <- 0 until m.nCols
+    yield
+      m.row(i).zip(m.row(j)).map(_ - _).sum