Add support for Observables to MESA (#2291)

Author: quaquel

codecov.yaml

@@ -7,7 +7,6 @@ coverage:
 
 ignore:
   - "benchmarks/**"
-  - "mesa/experimental/**"
   - "mesa/visualization/**"
 
 comment: off

mesa/experimental/__init__.py

@@ -1,5 +1,5 @@
 """Experimental init."""
 
-from mesa.experimental import cell_space, devs
+from mesa.experimental import cell_space, devs, mesa_signals
 
-__all__ = ["cell_space", "devs"]
+__all__ = ["cell_space", "devs", "mesa_signals"]

mesa/experimental/mesa_signals/__init__.py

@@ -0,0 +1,13 @@
+"""Functionality for Observables."""
+
+from .mesa_signal import All, Computable, Computed, HasObservables, Observable
+from .observable_collections import ObservableList
+
+__all__ = [
+    "Observable",
+    "ObservableList",
+    "HasObservables",
+    "All",
+    "Computable",
+    "Computed",
+]