This patch adds the new **executor-side resolver API** as suggested by
@lhames. It introduces a `DylibSymbolResolver` that helps resolve
symbols for each loaded dylib.

Previously, we returned a `DylibHandle` to the controller. Now, we wrap
the native handle inside `DylibSymbolResolver` and return a
`ResolverHandle` instead. This makes the code cleaner and separates the
symbol resolution logic from raw handle management.