feat: make metadata receipts optional

Receipts are almost unused other than returning the nonce of the from
field for deposit transactions. This change makes the entire receipts
field optional for flashblocks. This means that deposit transactions
will not return a nonce from the RPC until the canonical block is
processed.

While this will change RPC behavior, it will decrease flashblock size
significantly, and the tradeoff of size vs a few hundred ms latency
to reading the nonce of a deposit transaction is easily worth it.

Author: meyer9

crates/flashblocks/src/processor.rs

@@ -333,7 +333,9 @@ where
                 .iter()
                 .map(|flashblock| flashblock.metadata.receipts.clone())
                 .fold(HashMap::default(), |mut acc, receipts| {
-                    acc.extend(receipts);
+                    if let Some(receipts) = receipts {
+                        acc.extend(receipts);
+                    }
                     acc
                 });
 

crates/flashtypes/src/metadata.rs

@@ -8,7 +8,7 @@ use serde::{Deserialize, Serialize};
 #[derive(Debug, Deserialize, Serialize, Clone, PartialEq, Default)]
 pub struct Metadata {
     /// Transaction receipts indexed by hash.
-    pub receipts: HashMap<B256, OpReceipt>,
+    pub receipts: Option<HashMap<B256, OpReceipt>>,
     /// Updated account balances.
     pub new_account_balances: HashMap<Address, U256>,
     /// Block number this flashblock belongs to.