Extending contrib module filelog service class displays PSR implementation error

I wanted to override the logger.filelog service from filelog module to make use of my own parser.

An error occurred through drush cim and drush cr when the new custom module that overrides the service is enabled.

The website encountered an unexpected error. Please try again later.
Symfony\Component\DependencyInjection\Exception\LogicException: Service 'logger.filelog' for consumer 'logger.factory' does not implement Psr\Log\LoggerInterface. in Drupal\Core\DependencyInjection\Compiler\TaggedHandlersPass->processServiceCollectorPass() (line 182 of /app/docroot/core/lib/Drupal/Core/DependencyInjection/Compiler/TaggedHandlersPass.php).

My custom modules structure looks like this

custom_module
  - src
    - Logger
      - TestFilelog.php
    CustomModuleServiceProvider.php
  custom_module.info.yml
  custom_module.module

Currently the service provider class has implemented ServiceModifierInterface and altered the original logger.filelog service by setting its class to Drupal\custom_module\Logger\TestFilelog.

/**
 * Class to override contrib module logger.filelog service.
 */
class CustomModuleServiceProvider implements ServiceModifierInterface {

  /**
   * {@inheritdoc}
   */
  public function alter(ContainerBuilder $container) {
    if ($container->has('logger.filelog')) {
      $definition = $container->getDefinition('logger.filelog');
      $definition->setClass('Drupal\custom_module\Logger\TestFilelog');
    }
  }

}

TestFilelog.php

namespace Drupal\custom_module\Logger;

use Drupal\filelog\Logger\FileLog;

/**
 * File-based logger.
 */
class TestFileLog extends FileLog {

  /**
   * Renders a message to a string.
   *
   * @param mixed $level
   *   Severity level of the log message.
   * @param string $message
   *   Content of the log message.
   * @param array $context
   *   Context of the log message.
   *
   * @return string
   *   The formatted message.
   */
  protected function render($level, $message, array $context = []): string {

    $plainString = parent::render($level, $message, $context);

    $custom_channel = [
      'filter_custom_channel'
    ];

    if (in_array($context['channel'], $custom_channel)) {
      $plainString = $this->parseStrMasking($plainString);
    }
    return $plainString;
  }

  /**
   * Mask personal details from strings to logs.
   *
   * @param string $pureString
   *   The string to be parsed.
   *
   * @return string
   *   The string that has been masked.
   */
  protected function parseStrMasking(string $pureString) {
    // Default to return finalString.
    $finalString = $pureString;
    
    // Custom parsing goes here.
    
    return $finalString;
  }

}

I see that Drupal\filelog\Logger\FileLog; has use RfcLoggerTrait; which does implement the Psr\Log\LoggerInterface, what am I missing here??