Optimization of Collision Group Script (#984)

## Changes

I've optimized the script for handling collision groups in Roblox. The
main change involves removing the connection to DescendantAdded,
applying the collision group immediately to all parts in the model upon
character addition. This reduces unnecessary event connections,
improving performance by applying the collision group once for all
descendants, rather than repeatedly when new parts are added. This
should help improve game performance, especially when handling many
parts or players.

## Checks

By submitting your pull request for review, you agree to the following:

- [x] This contribution was created in whole or in part by me, and I
have the right to submit it under the terms of this repository's open
source licenses.
- [x] I understand and agree that this contribution and a record of it
are public, maintained indefinitely, and may be redistributed under the
terms of this repository's open source licenses.
- [x] To the best of my knowledge, all proposed changes are accurate.

---------

content/en-us/workspace/collisions.md

@@ -262,27 +262,27 @@ interesting but unintended gameplay, such as characters jumping on top of each o
 local PhysicsService = game:GetService("PhysicsService")
 local Players = game:GetService("Players")
 
-PhysicsService:RegisterCollisionGroup("Characters")
-PhysicsService:CollisionGroupSetCollidable("Characters", "Characters", false)
-
-local function onDescendantAdded(descendant)
-	-- Set collision group for any part descendant
-	if descendant:IsA("BasePart") then
-		descendant.CollisionGroup = "Characters"
+local CollisionGroupName = "Characters"
+PhysicsService:RegisterCollisionGroup(CollisionGroupName)
+PhysicsService:CollisionGroupSetCollidable(CollisionGroupName, CollisionGroupName, false)
+
+local function setCollisionGroup(model)
+	-- Apply collision group to all existing parts in the model
+	for _, descendant in model:GetDescendants() do
+		if descendant:IsA("BasePart") then
+			descendant.CollisionGroup = CollisionGroupName
+		end
 	end
 end
 
-local function onCharacterAdded(character)
-	-- Process existing and new descendants for physics setup
-	for _, descendant in character:GetDescendants() do
-		onDescendantAdded(descendant)
-	end
-	character.DescendantAdded:Connect(onDescendantAdded)
-end
-
 Players.PlayerAdded:Connect(function(player)
-	-- Detect when the player's character is added
-	player.CharacterAdded:Connect(onCharacterAdded)
+	player.CharacterAdded:Connect(function(character)
+		setCollisionGroup(character)
+	end)
+	-- If the player already has a character, apply the collision group immediately
+	if player.Character then
+		setCollisionGroup(player.Character)
+	end
 end)
 ```
 
@@ -360,4 +360,4 @@ The `Class.TriangleMeshPart.CollisionFidelity|CollisionFidelity` property has th
 To view collision fidelity in Studio, toggle on **Collision fidelity** from the [Visualization Options](../studio/ui-overview.md#visualization-options) widget in the upper‑right corner of the 3D viewport.
 </Alert>
 
-For more information on the performance impact of collision fidelity options and how to mitigate them, see [Performance Optimization](../performance-optimization/improving.md#physics-computation). For an in‑depth walkthrough on how to choose a collision fidelity option that balances your precision needs and performance requirements, see [here](../tutorials/environmental-art/assemble-an-asset-library.md#collisionfidelity).
+For more information on the performance impact of collision fidelity options and how to mitigate them, see [Performance Optimization](../performance-optimization/improving.md#physics-computation).