Returns the name of the given source.

def get_source_name(self, src_id):
        """Returns the name of the given source."""
        len_out = _ffi.new('unsigned int *')
        rv = rustcall(_lib.lsm_view_get_source_name,
                      self._get_ptr(), src_id, len_out)
        if rv:
            return decode_rust_str(rv, len_out[0])