fix(ev-deployer): make [contracts] section optional in config

Default to an empty ContractsConfig when the section is omitted,
so a minimal config only needs [chain].

Author: randygrok

bin/ev-deployer/src/config.rs

@@ -11,6 +11,7 @@ pub(crate) struct DeployConfig {
     /// Chain configuration.
     pub chain: ChainConfig,
     /// Contract configurations.
+    #[serde(default)]
     pub contracts: ContractsConfig,
 }
 
@@ -23,7 +24,7 @@ pub(crate) struct ChainConfig {
 }
 
 /// All contract configurations.
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Deserialize, Default)]
 pub(crate) struct ContractsConfig {
     /// `AdminProxy` contract config (optional).
     pub admin_proxy: Option<AdminProxyConfig>,
@@ -94,6 +95,17 @@ owner = "0x0000000000000000000000000000000000000000"
         assert!(config.validate().is_err());
     }
 
+    #[test]
+    fn no_contracts_section() {
+        let toml = r#"
+[chain]
+chain_id = 1
+"#;
+        let config: DeployConfig = toml::from_str(toml).unwrap();
+        config.validate().unwrap();
+        assert!(config.contracts.admin_proxy.is_none());
+    }
+
     #[test]
     fn admin_proxy_only() {
         let toml = r#"