Only log class name on ToolCallingAutoConfiguration#ClassNotFoundException in getClassOrNull

Fixes #4205
Fixes #4249

The getClassOrNull method is designed to gracefully handle missing classes
by returning null, but was logging full stack traces for ClassNotFoundException
which could mislead users into thinking there's an actual problem.

Changes:
- Log only the class name when ClassNotFoundException occurs
- Add type safety check for RuntimeException subclasses
- Add separate handling for other exceptions with full stack trace
- Improve log message clarity to reduce user confusion

This maintains the expected behavior while providing cleaner, less alarming
log output for normal class-not-found scenarios.

Signed-off-by: Sun Yuhan <[email protected]>
(cherry picked from commit befaf87)

Author: sunyuhan1998

auto-configurations/models/tool/spring-ai-autoconfigure-model-tool/src/main/java/org/springframework/ai/model/tool/autoconfigure/ToolCallingAutoConfiguration.java

@@ -125,10 +125,19 @@ ToolCallingContentObservationFilter toolCallingContentObservationFilter() {
 
 	private static Class<? extends RuntimeException> getClassOrNull(String className) {
 		try {
-			return (Class<? extends RuntimeException>) ClassUtils.forName(className, null);
+			Class<?> clazz = ClassUtils.forName(className, null);
+			if (RuntimeException.class.isAssignableFrom(clazz)) {
+				return (Class<? extends RuntimeException>) clazz;
+			}
+			else {
+				logger.debug("Class {} is not a subclass of RuntimeException", className);
+			}
 		}
 		catch (ClassNotFoundException e) {
-			logger.debug("Cannot load class", e);
+			logger.debug("Cannot load class: {}", className);
+		}
+		catch (Exception e) {
+			logger.debug("Error loading class: {}", className, e);
 		}
 		return null;
 	}