wip: refactor into fewer crates

crates/engine/src/clock.rs

@@ -0,0 +1,16 @@
+mod clock_api;   pub use self::clock_api::*;
+mod clock_model; pub use self::clock_model::*;
+
+pub trait HasClock: Send + Sync {
+    fn clock (&self) -> &Clock;
+    fn clock_mut (&mut self) -> &mut Clock;
+}
+
+#[macro_export] macro_rules! has_clock {
+    (|$self:ident:$Struct:ident$(<$($L:lifetime),*$($T:ident$(:$U:path)?),*>)?|$cb:expr) => {
+        impl $(<$($L),*$($T $(: $U)?),*>)? HasClock for $Struct $(<$($L),*$($T),*>)? {
+            fn clock (&$self) -> &Clock { &$cb }
+            fn clock_mut (&mut $self) -> &mut Clock { &mut $cb }
+        }
+    }
+}