feat: Simplify router encoder

Don't make selector() a member of the StrategyEncoder trait. It is needed only for certain strategies. The strategy should manage it itself.

--- don't change below this line ---
ENG-4081 Took 17 minutes

src/encoding/strategy_encoder.rs

@@ -9,7 +9,6 @@ pub trait StrategyEncoder {
         to_encode: Solution,
         router_address: Bytes,
     ) -> Result<Vec<u8>, EncodingError>;
-    fn selector(&self, exact_out: bool) -> &str;
 }
 
 pub trait StrategySelector {