Do not preprocess COW AMMs when not configured (#3925)

# Description
When the driver's COW AMM config is empty, the corresponding task still
tries to search for surplus capturing jit order owners among the AMMs
and fires a redundant warning log in that case. When the driver doesn't
expect any AMMs, this log doesn't make any sense. This PR fixes this.

# Changes

- [ ] Make the COW AMM cache optional based on the COW AMMs config.
- [ ] When None, return fast with no AMMs for every auction with no
redundant logs.

## How to test
Logs on chains where COW AMMs are not configured.

## Related Issues

Fixes #3890

Author: squadgazzz

crates/driver/src/domain/competition/pre_processing.rs

@@ -60,7 +60,7 @@ pub struct Utilities {
     liquidity_fetcher: infra::liquidity::Fetcher,
     tokens: tokens::Fetcher,
     balance_fetcher: Arc<dyn BalanceFetching>,
-    cow_amm_cache: cow_amm::Cache,
+    cow_amm_cache: Option<cow_amm::Cache>,
 }
 
 impl std::fmt::Debug for Utilities {
@@ -390,12 +390,16 @@ impl Utilities {
     }
 
     async fn cow_amm_orders(self: Arc<Self>, auction: Arc<Auction>) -> Arc<Vec<Order>> {
+        let Some(ref cow_amm_cache) = self.cow_amm_cache else {
+            // CoW AMMs are not configured, return empty vec
+            return Default::default();
+        };
+
         let _timer = metrics::get().processing_stage_timer("cow_amm_orders");
         let _timer2 =
             observe::metrics::metrics().on_auction_overhead_start("driver", "cow_amm_orders");
 
-        let cow_amms = self
-            .cow_amm_cache
+        let cow_amms = cow_amm_cache
             .get_or_create_amms(&auction.surplus_capturing_jit_order_owners)
             .await;
 

crates/driver/src/domain/cow_amm.rs

@@ -24,7 +24,11 @@ pub struct Cache {
 }
 
 impl Cache {
-    pub fn new(web3: DynProvider, factory_mapping: HashMap<Address, Address>) -> Self {
+    pub fn new(web3: DynProvider, factory_mapping: HashMap<Address, Address>) -> Option<Self> {
+        if factory_mapping.is_empty() {
+            return None;
+        }
+
         let helper_by_factory = factory_mapping
             .into_iter()
             .map(|(factory, helper)| {
@@ -34,11 +38,11 @@ impl Cache {
                 )
             })
             .collect();
-        Self {
+        Some(Self {
             inner: RwLock::new(HashMap::new()),
             web3: web3.clone(),
             helper_by_factory,
-        }
+        })
     }
 
     /// Gets or creates AMM instances for the given surplus capturing JIT order