dev: Make routing generic

[akhercha]

Current Behavior

For the endpoints:

• get_entry
• onchain/get_entry
• onchain/get_history
  We use a routing mechanism, allowing us to find alternatives routes for a pair. The code is really similar and currently just repeated in the 3 modules.

Expected Behavior

We should make it unique so it works for the 3 use cases (using a Trait?).