Watch for lodestone (#2146)

* use `watch` to avoid busy-waiting for the bit seed to grow

Prompted by #2140, which shows hundreds of `ishere` calls.

| Before | After |
|--------|--------|
| <img width="143" alt="Screenshot 2024-09-15 at 10 02 51 PM" src="https://github.com/user-attachments/assets/174827e4-9371-4405-a6c2-dd20233e4588"> | <img width="143" alt="Screenshot 2024-09-15 at 10 01 32 PM" src="https://github.com/user-attachments/assets/a1d02d16-487c-46d0-b5f1-5aaf4da111cb"> |

This should make the testing scenario take 0.1s from previous 0.5s. You can test it with:
```sh
cabal run swarm-integration -O0 -- -p '/Testing\/562-lodestone/
```

data/scenarios/Testing/562-lodestone.sw

@@ -5,8 +5,10 @@ def ifC = \p.\t.\e.
   if b t e
 end;
 
-def until = \p.\t.
-  ifC p t {until p t}
+def waitFor = \e.\t.
+  watch down;
+  wait 100;
+  ifC (ishere e) t {waitFor e t}
 end;
 
 def repeat = \c.
@@ -29,18 +31,18 @@ end;
 
 // get one lodestone
 build {log "Hey!"; turn north; m2; l <- grab; turn back; m2; place l};
-until (ishere "lodestone") {grab};
+waitFor "lodestone" {grab};
 
 // get two bit (0)
 build {
   log "Hi!";
   repeat (
     log "I am going for a bit";
-    turn east; m2; x <- until (ishere "bit (0)") {harvest}; turn back; m2; place x;
+    turn east; m2; x <- waitFor "bit (0)" {harvest}; turn back; m2; place x;
 		log "I brought a bit";
 )};
-until (ishere "bit (0)") {grab};
-until (ishere "bit (0)") {grab};
+waitFor "bit (0)" {grab};
+waitFor "bit (0)" {grab};
 
 make "bit (1)";
 make "drill bit"

data/scenarios/Testing/562-lodestone.yaml

@@ -25,6 +25,7 @@ robots:
       - workbench
       - 3D printer
       - branch predictor
+      - rolex
     inventory:
       - [10, drill]
       - [10, lambda]
@@ -37,6 +38,7 @@ robots:
       - [10, strange loop]
       - [10, branch predictor]
       - [10, toolkit]
+      - [10, rolex]
       - [0, drill bit]
       - [0, bit (0)]
       - [0, bit (1)]