round+executor: Use finer-grained state machine events

[romac]

Based on this diff by @ancazamfir:

diff --git a/Code/round/src/state_machine.rs b/Code/round/src/state_machine.rs
index fc6c7ad..4bafc68 100644
--- a/Code/round/src/state_machine.rs
+++ b/Code/round/src/state_machine.rs
@@ -99,12 +99,12 @@ pub fn apply_event(mut state: State, round: Round, event: Event) -> Transition {
         // From Prevote. Event must be for current round.
         (Step::Prevote, Event::PolkaAny) if this_round => schedule_timeout_prevote(state), // L34
         (Step::Prevote, Event::PolkaNil) if this_round => precommit_nil(state),            // L44
-        (Step::Prevote, Event::PolkaValue(value_id)) if this_round => precommit(state, value_id), // L36/L37 - NOTE: only once?
+        (Step::Prevote, Event::ProposalAndPolkaCurrent(value)) if this_round => precommit(state, value), // L36/L37 - NOTE: only once?
         (Step::Prevote, Event::TimeoutPrevote) if this_round => precommit_nil(state), // L61

         // From Precommit. Event must be for current round.
-        (Step::Precommit, Event::PolkaValue(value_id)) if this_round => {
-            set_valid_value(state, value_id)
+        (Step::Precommit, Event::ProposalAndPolkaCurrent(value)) if this_round => {
+            set_valid_value(state, value)
:
-    TimeoutPrevote,          // Timeout waiting for prevotes.
-    TimeoutPrecommit,        // Timeout waiting for precommits.
+    NewRound,                // Start a new round, not as proposer.L20
+    NewRoundProposer(Value), // Start a new round and propose the Value.L14
+    Proposal(Proposal),      // Receive a proposal. L22 + L23 (valid)
+    ProposalAndPolkaPrevious(Value), // Recieved a proposal and a polka value from a previous round. L28 + L29 (valid)
+    ProposalInvalid,         // Receive an invalid proposal. L26 + L32 (invalid)
+    PolkaAny,                // Receive +2/3 prevotes for anything. L34
+    PolkaNil,                // Receive +2/3 prevotes for nil. L44
+    ProposalAndPolkaCurrent(Value),     // Receive +2/3 prevotes for Value in current round. L36
+    PrecommitAny,            // Receive +2/3 precommits for anything. L47
+    ProposalAndPrecommitValue(Value), // Receive +2/3 precommits for Value. L49
+    RoundSkip,               // Receive +1/3 messages from a higher round. OneCorrectProcessInHigherRound, L55
+    TimeoutPropose,          // Timeout waiting for proposal. L57
+    TimeoutPrevote,          // Timeout waiting for prevotes. L61
+    TimeoutPrecommit,        // Timeout waiting for precommits. L65
 }

[romac]

Done in #19