Replace the remaining schedulers with AgentSet functionality (#202)

This PR completes the migration from schedulers to AgentSet functionality across the mesa-examples repository for all regular (non-`gis`/-`rl`) examples. Key changes include:

- Replaced `RandomActivation`, `SimultaneousActivation`, and `RandomActivationByType` schedulers with appropriate AgentSet methods
- Updated `Model.step()` implementations to use AgentSet activation
- Removed references to `schedule.steps`, `schedule.agents`, and `schedule.agents_by_type`
- Updated agent addition/removal logic to work with AgentSets
- Adjusted data collection and visualization code to use `Model.steps` and `Model.agents`

For more details on migrating from schedulers to AgentSets, see the migration guide: https://mesa.readthedocs.io/en/latest/migration_guide.html#time-and-schedulers

examples/wolf_sheep/wolf_sheep/test_random_walk.py

@@ -5,7 +5,6 @@
 
 from mesa import Model
 from mesa.space import MultiGrid
-from mesa.time import RandomActivation
 from mesa.visualization.TextVisualization import TextGrid, TextVisualization
 from wolf_sheep.random_walk import RandomWalker
 
@@ -40,17 +39,15 @@ def __init__(self, width, height, agent_count):
         self.grid = MultiGrid(self.width, self.height, torus=True)
         self.agent_count = agent_count
 
-        self.schedule = RandomActivation(self)
         # Create agents
         for i in range(self.agent_count):
             x = self.random.randrange(self.width)
             y = self.random.randrange(self.height)
             a = WalkerAgent(i, (x, y), self, True)
-            self.schedule.add(a)
             self.grid.place_agent(a, (x, y))
 
     def step(self):
-        self.schedule.step()
+        self.agents.shuffle_do("step")
 
 
 class WalkerWorldViz(TextVisualization):