Set default fallback duration to MAX. (#3905)

## Motivation

The validators are not currently expected to start client processes
automatically. So chains that enter fallback mode are effectively
bricked.

## Proposal

Set the default fallback timeout to `MAX`, so validators will never sign
a fallback timeout certificate.

## Test Plan

(Only a default chain config change.)

## Release Plan

- Nothing to do / These changes follow the usual release cycle.

## Links

- [reviewer
checklist](https://github.com/linera-io/linera-protocol/blob/main/CONTRIBUTING.md#reviewer-checklist)

Author: afck

linera-base/src/identifiers.rs

@@ -1018,7 +1018,7 @@ mod tests {
         );
         assert_eq!(
             description.id().to_string(),
-            "f8c2f02adc0ac763ffd74a32d02aa37490d869605c356a2da55e1d09e7d253bf"
+            "0e94923a8f72ef1d0e69e6958e655002f2b1883bac9a67a4704d2f4125825217"
         );
     }
 

linera-base/src/ownership.rs

@@ -41,7 +41,9 @@ impl Default for TimeoutConfig {
             fast_round_duration: None,
             base_timeout: TimeDelta::from_secs(10),
             timeout_increment: TimeDelta::from_secs(1),
-            fallback_duration: TimeDelta::from_secs(60 * 60 * 24),
+            // This is `MAX` because the validators are not currently expected to start clients for
+            // every chain with an old tracked message in the inbox.
+            fallback_duration: TimeDelta::MAX,
         }
     }
 }

linera-core/src/unit_tests/worker_tests.rs

@@ -184,12 +184,22 @@ where
         index: u32,
         owner: AccountOwner,
         balance: Amount,
+    ) -> ChainDescription {
+        self.add_root_chain_with_ownership(index, balance, ChainOwnership::single(owner))
+            .await
+    }
+
+    async fn add_root_chain_with_ownership(
+        &mut self,
+        index: u32,
+        balance: Amount,
+        ownership: ChainOwnership,
     ) -> ChainDescription {
         let origin = ChainOrigin::Root(index);
         let config = InitialChainConfig {
             admin_id: Some(self.admin_id()),
             epoch: self.admin_description.config().epoch,
-            ownership: ChainOwnership::single(owner),
+            ownership,
             committees: self.admin_description.config().committees.clone(),
             balance,
             application_permissions: Default::default(),
@@ -3560,7 +3570,12 @@ where
     let public_key = signer.generate_new();
     let mut env = TestEnvironment::new(storage, false, false).await;
     let balance = Amount::from_tokens(5);
-    let chain_1_desc = env.add_root_chain(1, public_key.into(), balance).await;
+    let mut ownership = ChainOwnership::single(public_key.into());
+    // Configure a fallback duration. (The default is `MAX`, i.e. never.)
+    ownership.timeout_config.fallback_duration = TimeDelta::from_secs(5);
+    let chain_1_desc = env
+        .add_root_chain_with_ownership(1, balance, ownership)
+        .await;
     let chain_id = chain_1_desc.id();
 
     // At time 0 we don't vote for fallback mode.