Add support for archive files

Each attachment is now first extracted into potentially multiple ones,
if it is recognized as an archive. This is the first step in
processing. The original archive file is also stored and the resulting
attachments are associated to their original archive.

First support is implemented for zip files.

modules/files/src/test/scala/docspell/files/ZipTest.scala

@@ -0,0 +1,30 @@
+package docspell.files
+
+import minitest._
+import cats.effect._
+import cats.implicits._
+import scala.concurrent.ExecutionContext
+
+object ZipTest extends SimpleTestSuite {
+
+  val blocker     = Blocker.liftExecutionContext(ExecutionContext.global)
+  implicit val CS = IO.contextShift(ExecutionContext.global)
+
+  test("unzip") {
+    val zipFile = ExampleFiles.letters_zip.readURL[IO](8192, blocker)
+    val uncomp = zipFile.through(Zip.unzip(8192, blocker))
+
+    uncomp.evalMap(entry => {
+      val x = entry.data.map(_ => 1).foldMonoid.compile.lastOrError
+      x.map(size => {
+        if (entry.name.endsWith(".pdf")) {
+          assertEquals(entry.name, "letter-de.pdf")
+          assertEquals(size, 34815)
+        } else {
+          assertEquals(entry.name, "letter-en.txt")
+          assertEquals(size, 1131)
+        }
+      })
+    }).compile.drain.unsafeRunSync
+  }
+}