145_Ray_Casting - optimice performance by using square distance

when using dist only for compare, its better to use the `square distance`. Because otherwise quare-root needs to be calculated which is much more cpu heavy.

https://github.com/CodingTrain/Coding-Challenges/blob/2a9d68112b1aa80cbd5aa303f1d97dda7b045fde/145_Ray_Casting/P5/particle.js#L29

開啟 145_Ray_Casting/P5/particle.js 的第 29 行，檢查 dist 如何用於比較。更新比較邏輯以使用距離的平方，然後驗證 ray-casting 範例仍然選取相同的結果，且行為正確。

由索引模型根據 Issue 內容生成。