The quick answer is no, you can't extend com.adobe.cq.wcm.core.components.models.contentfragment.ContentFragmentList, for two reasons:
It's an interface (which allows extension, but that yon't help you implement pagination)
The actual implementation, com.adobe.cq.wcm.core.components.internal.models.v1.contentfragment.ContentFragmentListImpl, is not exported in OSGi, so if you extend it and deploy your bundle, you'll get a dependency error.
If you want to "extend" the behavior of the you'll have to use the Delegation Pattern. You can find a tutorial explaining this pattern in AEM here. If you are using Lombok (and I think you should), you can use their @Delegate annotation to reduce on boilerplate code.
However, I assume that you are thinking of pagination as a front-end process (ie: no need to reload the entire page when you go from page 1 to page 2)? In that case, you'll have to implement the pagination logic in JS (using a web component for example, I recommend https://open-wc.org/). Then create a Sling Servletor Model that you can call to get X results at a time.