NoClassDefFoundError for org.apache.logging.log4j.spi.ExtendedLogger in Tomcat 11 with Java 21

### Problem Description
Our web application, which runs in Tomcat 11 and Java 21, uses **SLF4J + Logback** for logging. However, it allows dynamically importing extensions along with JARs at runtime using the server **classloader**. One of these extensions depends on `log4j-api-2.17.1.jar`, which is correctly present in the classpath.

After deploying the extension, **calling a service that uses Log4j results in the following error:**

`java.lang.NoClassDefFoundError: org/apache/logging/log4j/spi/ExtendedLogger`

The error mentioned above is being received by executing this line `Logger logger = LogManager.getLogger();` in extension service.

However, other Log4j classes, such as `LogManager` and `Logger`, are loading without issues.

### Environment Details

- **Application Type** : WAR-based Java web application

- **Application Server** : Apache Tomcat 11

- **Java Version** : 21

- **Logging Framework in Main App** : SLF4J with Logback

- **Extension Support** : Allows dynamic loading of JARs at runtime using the server classloader

- **Problematic Dependency** : log4j-api-2.17.1.jar (used by an extension)

### Debugging Steps & Findings

1. Verified that `log4j-api-2.17.1.jar` is present in the classpath and contains `org/apache/logging/log4j/spi/ExtendedLogger.class`.
2. Checked for multiple versions of `log4j-api` dependency in our application. **Result** : Only one instance of log4j-api-2.17.1.jar is found.
3. Printed the class loaders for Log4j classes:
```
System.out.println(org.apache.logging.log4j.LogManager.class);
System.out.println(org.apache.logging.log4j.Logger.class);
System.out.println(org.apache.logging.log4j.spi.ExtendedLogger.class);
```
**Result**:
`LogManager` and `Logger` printed correctly.
`ExtendedLogger.class` throws `NoClassDefFoundError`.

### Additional Notes

- **Same application worked in Tomcat 9 without requiring a restart.**

- **Tomcat 11 requires a restart for `ExtendedLogger` to be found.**

- **After restarting Tomcat 11, everything works correctly.**

### Request for Help

We need guidance on :

- Why is `ExtendedLogger` missing, even though other Log4j classes load fine?

- Does Tomcat 11’s classloader affect Log4j differently compared to Tomcat 9?

- Are there additional configurations we should try in Tomcat 11?

Would appreciate any insights from the community!

Start with the extension service call to `LogManager.getLogger()` in the Tomcat 11, Java 21 WAR deployment, then compare class loading before and after a restart. Investigate the dynamically loaded `log4j-api-2.17.1.jar` and the reported `ExtendedLogger` failure; done means explaining the difference from Tomcat 9 and identifying any required configuration or reproducible project change.

Written by the indexing model from the issue text.