docs: More docs and improvements of existing docs

- Tried not to leave a single public function undocumented, though did not double-document public function with obvious names
- Remove all mentions of the strategy selector in favour of the strategy registry (to avoid confusion)

src/encoding/strategy_encoder.rs

@@ -2,6 +2,7 @@ use tycho_core::{models::Chain, Bytes};
 
 use crate::encoding::{errors::EncodingError, models::Solution, swap_encoder::SwapEncoder};
 
+/// Encodes a solution using a specific strategy.
 pub trait StrategyEncoder {
     fn encode_strategy(
         &self,