fix: Don't leak evm specific code to interfaces(PrivateKeySigner, Chain)

Pass the signer's private key as a string around and only create a PrivateKeySigner inside Permit2 (where it's needed)
Use tycho-core Chain instead of Alloy ChainID. Create a temp method to convert between them
Create a EVMSwapEncoder that implements the executor_selector (that is evm specific)

--- don't change below this line ---
ENG-4081 Took 1 hour 7 minutes

src/encoding/strategy_encoder.rs

@@ -1,6 +1,4 @@
-use alloy::signers::local::PrivateKeySigner;
-use alloy_primitives::ChainId;
-use tycho_core::Bytes;
+use tycho_core::{models::Chain, Bytes};
 
 use crate::encoding::{errors::EncodingError, models::Solution};
 
@@ -19,7 +17,7 @@ pub trait StrategySelector {
     fn select_strategy(
         &self,
         solution: &Solution,
-        signer: Option<PrivateKeySigner>,
-        chain_id: ChainId,
+        signer_pk: Option<String>,
+        chain_id: Chain,
     ) -> Result<Box<dyn StrategyEncoder>, EncodingError>;
 }