[topo] Remove im-rc dep and move __reset hack into a separate root! macro.

`topo::Point::__enter_child` -> `topo::__enter_child`, which allows us to make `Point` private to the crate.

`topo::Point::__reset`/`topo::__reset` -> `topo::root!` which is an analog to `topo::call!` but also leaves the parent state intact after calling the inner expression.

Author: anp

src/lib.rs

@@ -118,7 +118,7 @@ pub async fn runloop(mut root: impl FnMut(&state::Key<LoopBehavior>)) {
     loop {
         current_revision.0 += 1;
 
-        topo::call!(|| {
+        topo::root!(|| {
             let (_, behavior) = state!((), |()| LoopBehavior::default());
 
             // CALLER'S CODE IS CALLED HERE
@@ -131,9 +131,6 @@ pub async fn runloop(mut root: impl FnMut(&state::Key<LoopBehavior>)) {
             Revision => current_revision
         });
 
-        // TODO break this by adding test with multiple identical runloops that clobber each other
-        topo::Point::__reset();
-
         match next_behavior.as_ref().unwrap().deref() {
             LoopBehavior::OnWake => {
                 trace!(target: "runloop_pending", revision = debug(&current_revision));

topo/Cargo.toml

@@ -5,7 +5,6 @@ authors = ["Adam Perry <adam.n.perry@gmail.com>"]
 edition = "2018"
 
 [dependencies]
-im-rc = "13"
 owning_ref = "0.4"
 tokio-trace = { version = "0.1", features = ["log"] }
 topo-macro = { path = "macro" }