Split reporter and case runner, use channels to pass test reports (#137)

* Use channels to send data to reporting thread and avoid hangs / mutex / duration. Limit max concurrent tasks to avoid too many open files

* More appropriate name for dirver/reporter task fns

* Back to parallelise individual cases, report individual cases, address grumbles

* newline before 'Failures' title in report

crates/config/src/lib.rs

@@ -96,10 +96,19 @@ pub struct Arguments {
     #[arg(long, default_value = "1")]
     pub number_of_nodes: usize,
 
-    /// Determines the amount of threads that will will be used.
-    #[arg(long, default_value = "12")]
+    /// Determines the amount of tokio worker threads that will will be used.
+    #[arg(
+        long,
+        default_value_t = std::thread::available_parallelism()
+            .map(|n| n.get())
+            .unwrap_or(1)
+    )]
     pub number_of_threads: usize,
 
+    /// Determines the amount of concurrent tasks that will be spawned to run tests. Defaults to 10 x the number of nodes.
+    #[arg(long)]
+    pub number_concurrent_tasks: Option<usize>,
+
     /// Extract problems back to the test corpus.
     #[arg(short, long = "extract-problems")]
     pub extract_problems: bool,
@@ -134,6 +143,13 @@ impl Arguments {
         panic!("should have a workdir configured")
     }
 
+    /// Return the number of concurrent tasks to run. This is provided via the
+    /// `--number-concurrent-tasks` argument, and otherwise defaults to --number-of-nodes * 20.
+    pub fn number_of_concurrent_tasks(&self) -> usize {
+        self.number_concurrent_tasks
+            .unwrap_or(20 * self.number_of_nodes)
+    }
+
     /// Try to parse `self.account` into a [PrivateKeySigner],
     /// panicing on error.
     pub fn wallet(&self) -> EthereumWallet {