Fix CI failures: javadoc + LAL setLayer codegen for non-enum Layer

- LayerExtension.java: javadoc inside `<pre>{@code ... @OverRide ...}</pre>`
  blew up because `{@code}` parses `@Override` as a nested unknown tag.
  Drop the `{@code}` wrapper and use HTML-escaped `&#64;Override` inside
  plain `<pre>`.

- LALBlockCodegen.generateFieldToOutput: previously detected enum-typed
  setters via `paramType.isEnum()` and emitted `Type.valueOf(string)` to
  cast LAL extractor `layer "MYSQL"` (a String literal) into the typed
  setter argument. With Layer no longer an enum, the `isEnum()` branch
  was missed and codegen tried to pass `String` to `setLayer(Layer)`,
  failing at compile-time. Add `paramType == Layer.class` to the same
  branch — Layer's registry-backed `valueOf(String)` keeps the call
  shape identical.

Author: wu-sheng

oap-server/analyzer/log-analyzer/src/main/java/org/apache/skywalking/oap/log/analyzer/v2/compiler/LALBlockCodegen.java

@@ -23,6 +23,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import org.apache.skywalking.oap.server.core.analysis.Layer;
 
 /**
  * Code generation for LAL block-level structures: {@code extractor},
@@ -265,7 +266,11 @@ private static void generateFieldToOutput(
             sb.append(", \"")
               .append(LALCodegenHelper.escapeJava(field.getFormatPattern()))
               .append("\")");
-        } else if (paramType.isEnum()) {
+        } else if (paramType.isEnum() || paramType == Layer.class) {
+            // `Layer` was historically an enum and is now a registry-backed value type with a
+            // matching `valueOf(String)`; both flow through the same `Type.valueOf(string)`
+            // codegen so LAL extractors written as `layer "MYSQL"` still resolve to the typed
+            // setter argument.
             sb.append(paramType.getName()).append(".valueOf(");
             LALValueCodegen.generateCastedValueAccess(sb, field.getValue(), "String", genCtx);
             sb.append(")");

oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/LayerExtension.java

@@ -33,15 +33,15 @@
  * {@code META-INF/services/org.apache.skywalking.oap.server.core.analysis.LayerExtension}.
  *
  * <p>Example:
- * <pre>{@code
+ * <pre>
  * public final class IotFleetLayers implements LayerExtension {
- *     @Override
+ *     &#64;Override
  *     public void contribute() {
  *         Layer.register("IOT_FLEET",   1000, true);
  *         Layer.register("IOT_GATEWAY", 1001, true);
  *     }
  * }
- * }</pre>
+ * </pre>
  *
  * <p>SPI is preferred over registering from a downstream module's {@code prepare()} because
  * Core's {@code prepare()} runs before every other module's {@code prepare()} — there is no