Add Optional Parameter for Algorithm Selection in `RouteInput`

We need to enhance `RouteInput` in `barq-common` to include an optional parameter for specifying a preferred routing algorithm.

This will allow users to force the use of a specific strategy during routing. If this parameter is not provided, the system should default to selecting the most suitable algorithm based on internal logic.

Start by locating RouteInput in barq-common and trace how routing algorithm selection currently happens. The change is complete when RouteInput accepts an optional preferred algorithm, uses it when provided, and preserves internal algorithm selection when it is absent.

Written by the indexing model from the issue text.