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

Author: EwoutH

examples/basic/schelling/analysis.ipynb

@@ -65,9 +65,9 @@
     }
    ],
    "source": [
-    "while model.running and model.schedule.steps < 100:\n",
+    "while model.running and model.steps < 100:\n",
     "    model.step()\n",
-    "print(model.schedule.steps)  # Show how many steps have actually run"
+    "print(model.steps)  # Show how many steps have actually run"
    ]
   },
   {
@@ -328,15 +328,15 @@
     "    Find the % of agents that only have neighbors of their same type.\n",
     "    \"\"\"\n",
     "    segregated_agents = 0\n",
-    "    for agent in model.schedule.agents:\n",
+    "    for agent in model.agents:\n",
     "        segregated = True\n",
     "        for neighbor in model.grid.iter_neighbors(agent.pos, True):\n",
     "            if neighbor.type != agent.type:\n",
     "                segregated = False\n",
     "                break\n",
     "        if segregated:\n",
     "            segregated_agents += 1\n",
-    "    return segregated_agents / model.schedule.get_agent_count()"
+    "    return segregated_agents / len(model.agents)"
    ]
   },
   {