Collection structs are missing readonly modifiers on methods, causing unnecessary defensive copy creation

How to reproduce:

1. Open the “GraphicsTesting.zip“ project
2. Open the “UnityStructsMissingReadonlyModifier.cs“ script in JetBrains Rider IDE
3. Observe the warnings on all of the methods

Expected result: No warnings about impure methods
Actual result: Impure method warnings are thrown

Reproducible in: 1.1.0, 2.6.2 (6000.0.60f1, 6000.2.8f1, 6000.3.0b7, 6000.4.0a3)

Reproduced on: Windows 11 Pro (24H2)
Not reproduced on: No other environment tested

Note: The warnings are not observable in Visual Studio 2022 or likely any other IDE