Use explicit class reference for resource loading in AbstractFileStore

[flying-musk]

In AbstractFileStore, the default resource is currently loaded with:

getClass().getResourceAsStream("/" + fileName)

Since AbstractFileStore is an abstract class, using getClass() makes the resource lookup depend on the runtime subclass.

A small improvement would be to replace it with:

AbstractFileStore.class.getResourceAsStream("/" + fileName)

This makes the lookup context explicit and stable, and should avoid inheritance-related ambiguity without changing the intended behavior.