feat: add ExecutionPayloadSidecar type (alloy-rs#1517)

* feat: add sidecar type

* feat: add ExecutionPayloadSidecar

* no-std

* clippy

crates/rpc-types-engine/src/lib.rs

@@ -13,6 +13,8 @@ extern crate alloc;
 
 mod cancun;
 pub use cancun::*;
+mod sidecar;
+pub use sidecar::*;
 
 mod forkchoice;
 pub use forkchoice::*;

crates/rpc-types-engine/src/sidecar.rs

@@ -0,0 +1,55 @@
+//! Contains helpers for dealing with additional parameters of `newPayload` requests.
+
+use crate::{CancunPayloadFields, MaybeCancunPayloadFields};
+use alloc::vec::Vec;
+use alloy_eips::eip7685::Requests;
+use alloy_primitives::B256;
+
+/// Container type for all available additional `newPayload` request parameters that are not present
+/// in the `ExecutionPayload` object itself.
+#[derive(Debug, Clone, Default)]
+pub struct ExecutionPayloadSidecar {
+    /// Cancun request params introduced in `engine_newPayloadV3` that are not present in the
+    /// `ExecutionPayload`.
+    cancun: MaybeCancunPayloadFields,
+    /// The EIP-7685 requests provided as additional request params to `engine_newPayloadV4` that
+    /// are not present in the `ExecutionPayload`.
+    prague: Option<Requests>,
+}
+
+impl ExecutionPayloadSidecar {
+    /// Returns a new empty instance (pre-cancun, v1, v2)
+    pub const fn none() -> Self {
+        Self { cancun: MaybeCancunPayloadFields::none(), prague: None }
+    }
+
+    /// Creates a new instance for cancun with the cancun fields for `engine_newPayloadV3`
+    pub fn v3(cancun: CancunPayloadFields) -> Self {
+        Self { cancun: cancun.into(), prague: None }
+    }
+
+    /// Creates a new instance post prague for `engine_newPayloadV4`
+    pub fn v4(cancun: CancunPayloadFields, requests: Requests) -> Self {
+        Self { cancun: cancun.into(), prague: Some(requests) }
+    }
+
+    /// Returns a reference to the [`CancunPayloadFields`].
+    pub const fn cancun(&self) -> Option<&CancunPayloadFields> {
+        self.cancun.as_ref()
+    }
+
+    /// Returns the parent beacon block root, if any.
+    pub fn parent_beacon_block_root(&self) -> Option<B256> {
+        self.cancun.parent_beacon_block_root()
+    }
+
+    /// Returns the blob versioned hashes, if any.
+    pub fn versioned_hashes(&self) -> Option<&Vec<B256>> {
+        self.cancun.versioned_hashes()
+    }
+
+    /// Returns the EIP-7685 requests
+    pub const fn requests(&self) -> Option<&Requests> {
+        self.prague.as_ref()
+    }
+}