feat: add util fns, change callback_selector to string, update first_swap check

src/encoding/evm/utils.rs

@@ -1,6 +1,6 @@
 use std::cmp::max;
 
-use alloy_primitives::{aliases::U24, Address, Keccak256, U256, U8};
+use alloy_primitives::{aliases::U24, keccak256, Address, FixedBytes, Keccak256, U256, U8};
 use num_bigint::BigUint;
 use tycho_core::Bytes;
 
@@ -91,3 +91,17 @@ pub fn get_token_position(tokens: Vec<Bytes>, token: Bytes) -> Result<U8, Encodi
     );
     Ok(position)
 }
+
+/// Pads a byte slice to a fixed size array with leading zeros.
+pub fn pad_to_fixed_size<const N: usize>(input: &[u8]) -> Result<[u8; N], EncodingError> {
+    let mut padded = [0u8; N];
+    let start = N - input.len();
+    padded[start..].copy_from_slice(input);
+    Ok(padded)
+}
+
+/// Encodes a function selector to a fixed size array of 4 bytes.
+pub fn encode_function_selector(selector: &str) -> FixedBytes<4> {
+    let hash = keccak256(selector.as_bytes());
+    FixedBytes::<4>::from([hash[0], hash[1], hash[2], hash[3]])
+}