Follow HTTP redirects (#328)

- Change HttpClient to follow all redirects except HTTPS to HTTP.
- Run language snippet tests with --no-cache and real PackageServer
  instead of pre-seeded cache.
  This increases HTTP test coverage and enables testing of package redirects.
- Change PackageServer to return 301 for request paths starting with /HTTP301/
  and 307 for request paths starting with /HTTP307/.
- Update some outdated test package checksums that apparently weren't verified.

pkl-commons-test/src/main/kotlin/org/pkl/commons/test/InputOutputTestEngine.kt

@@ -51,6 +51,10 @@ abstract class InputOutputTestEngine :
 
   protected abstract fun generateOutputFor(inputFile: Path): Pair<Boolean, String>
 
+  protected open fun beforeAll() {}
+
+  protected open fun afterAll() {}
+
   class ExecutionContext : EngineExecutionContext
 
   override fun getId(): String = this::class.java.simpleName
@@ -78,7 +82,17 @@ abstract class InputOutputTestEngine :
         (classSelectors.isEmpty() || classSelectors.any { it.className == className })
     ) {
 
-      val rootNode = InputDirNode(uniqueId, inputDir, ClassSource.from(testClass.java))
+      val rootNode =
+        object : InputDirNode(uniqueId, inputDir, ClassSource.from(testClass.java)) {
+          override fun before(context: ExecutionContext): ExecutionContext {
+            beforeAll()
+            return context
+          }
+
+          override fun after(context: ExecutionContext) {
+            afterAll()
+          }
+        }
       return doDiscover(rootNode, uniqueIdSelectors)
     }
 
@@ -124,7 +138,11 @@ abstract class InputOutputTestEngine :
 
   override fun createExecutionContext(request: ExecutionRequest) = ExecutionContext()
 
-  private inner class InputDirNode(uniqueId: UniqueId, val inputDir: Path, source: TestSource) :
+  private open inner class InputDirNode(
+    uniqueId: UniqueId,
+    val inputDir: Path,
+    source: TestSource
+  ) :
     AbstractTestDescriptor(uniqueId, inputDir.fileName.toString(), source), Node<ExecutionContext> {
     override fun getType() = Type.CONTAINER
   }

pkl-commons-test/src/main/kotlin/org/pkl/commons/test/PackageServer.kt

@@ -130,11 +130,23 @@ class PackageServer : AutoCloseable {
       return@HttpHandler
     }
     val path = exchange.requestURI.path
+    if (path.startsWith("/HTTP301/")) {
+      exchange.responseHeaders.add("Location", path.removePrefix("/HTTP301"))
+      exchange.sendResponseHeaders(301, -1)
+      exchange.close()
+      return@HttpHandler
+    }
+    if (path.startsWith("/HTTP307/")) {
+      exchange.responseHeaders.add("Location", path.removePrefix("/HTTP307"))
+      exchange.sendResponseHeaders(307, -1)
+      exchange.close()
+      return@HttpHandler
+    }
     val localPath =
       if (path.endsWith(".zip")) packagesDir.resolve(path.drop(1))
       else packagesDir.resolve("${path.drop(1)}${path}.json")
     if (!Files.exists(localPath)) {
-      exchange.sendResponseHeaders(404, 0)
+      exchange.sendResponseHeaders(404, -1)
       exchange.close()
       return@HttpHandler
     }