Merge pull request #33146: #33145 cache namespace string key in FlinkStateInternals

Author: je-ik

.github/trigger_files/beam_PostCommit_Java_Nexmark_Flink.json

@@ -0,0 +1,4 @@
+{
+  "comment": "Modify this file in a trivial way to cause this test suite to run",
+  "runFor": "#33146"
+}

.github/trigger_files/beam_PostCommit_Java_ValidatesRunner_Flink.json

@@ -1,5 +1,4 @@
 {
   "comment": "Modify this file in a trivial way to cause this test suite to run",
-  "https://github.com/apache/beam/pull/31156": "noting that PR #31156 should run this test",
-  "https://github.com/apache/beam/pull/32648": "testing addition of Flink 1.19 support"
+  "runFor": "#33146"
 }

runners/core-java/src/main/java/org/apache/beam/runners/core/StateNamespaces.java

@@ -90,8 +90,8 @@ public void appendTo(Appendable sb) throws IOException {
   /** {@link StateNamespace} that is scoped to a specific window. */
   public static class WindowNamespace<W extends BoundedWindow> implements StateNamespace {
 
-    private Coder<W> windowCoder;
-    private W window;
+    private final Coder<W> windowCoder;
+    private final W window;
 
     private WindowNamespace(Coder<W> windowCoder, W window) {
       this.windowCoder = windowCoder;