Add line breakdown API

We're using pprof query API in order to get breakdown by lines for a specific function. This approach is quite limited (it does not work in sandwich view, and can't be used for e.g., call graphs) and may cause performance issues. See [the issue](https://github.com/grafana/pyroscope-app-plugin/issues/372#issuecomment-2003122266) (private) in the app plugin repositry for details.

I propose to add use-case specific API that retrieves per line/location statistics for a given call site or function.