event_graph: introduce layers to the DAG

Each event corresponds to a specific layer(height) in the dag, making identifying and preventing cycles way easier, as all parents must exist in previous layers. Additionally, propagation and sync gremlins have been eliminated, and proper validations added

tests/consensus_prop.rs

@@ -29,7 +29,7 @@ use darkfi_sdk::{
     pasta::pallas,
 };
 use halo2_proofs::dev::MockProver;
-use log::info;
+use log::{info, warn};
 use rand::rngs::OsRng;
 
 pub const SECRET_KEY_PREFIX: pallas::Base = pallas::Base::from_raw([4, 0, 0, 0]);
@@ -46,14 +46,21 @@ pub const HEADSTART: pallas::Base = pallas::Base::from_raw([
 
 #[test]
 fn consensus_prop() -> Result<()> {
-    simplelog::TermLogger::init(
+    let mut cfg = simplelog::ConfigBuilder::new();
+    // We check this error so we can execute same file tests in parallel,
+    // otherwise second one fails to init logger here.
+    if simplelog::TermLogger::init(
         simplelog::LevelFilter::Info,
+        //simplelog::LevelFilter::Debug,
         //simplelog::LevelFilter::Trace,
-        simplelog::ConfigBuilder::new().build(),
+        cfg.build(),
         simplelog::TerminalMode::Mixed,
         simplelog::ColorChoice::Auto,
     )
-    .unwrap();
+    .is_err()
+    {
+        warn!(target: "test_harness", "Logger already initialized");
+    }
 
     let input_serial = pallas::Base::from(pallas::Base::from(10));
     //let input_serial = pallas::Base::from(pallas::Base::from(2));