feat: support custom Python EnvironmentObject subclasses

[YJack0000]

Summary

• Add pybind11 trampoline class to enable Python subclassing of EnvironmentObject
• Add generic add_object/remove_object methods to Environment
• Custom objects participate in the simulation loop via postIteration() override
• Custom objects are spatially indexed and appear in get_all_objects()

Usage Example (Python)

from simevopy import Environment, EnvironmentObject

class Obstacle(EnvironmentObject):
    def __init__(self):
        super().__init__(0, 0)
        self.damage = 10

    def post_iteration(self):
        pass  # obstacles don't move

class Trap(EnvironmentObject):
    def __init__(self):
        super().__init__(0, 0)
        self.triggered = False

    def post_iteration(self):
        pass

env = Environment(1000, 1000)
env.add_object(Obstacle(), 500, 500)
env.add_object(Trap(), 300, 300)

Discussion Points

• Custom objects 會出現在 get_all_objects() 中，但不會出現在 get_all_organisms() 或 get_all_foods() 中
• 目前 custom objects 在 spatial index 中有位置，所以會被 organism 的 react()/interact() 看到。如果搭配 PR3 的 custom strategy，Python 端可以根據 object type 自定義互動行為
• postIteration() 會在每個 tick 被呼叫，可以用來實作會隨時間變化的地圖物件（如消失的牆壁、移動的障礙物）
• 如果 postIteration() 需要回呼 Python，目前的單線程 postIteration 迴圈是安全的

Test plan

• All 3 existing Python tests pass
• Custom Python EnvironmentObject can be created, added, and removed
• Verify custom objects are visible in organism react/interact phase
• Test postIteration override from Python

🤖 Generated with Claude Code