Add quick save stack experimental feature.

[CooperCorona]

Mark the type contribution you are making:

• [x ] Experimental feature (new functionality that can be selectively enabled/disabled)
• Bug fix (non-breaking change which fixes an issue)

Description

Add an experimental feature that lets you have multiple quick save states at once, up to a user-configurable limit. Creating a new quick save when already at the limit removes the oldest quick save (the first in the collection view).

In my experience using Delta, I want to create speculative save states a lot. But opening the menu, selecting save states, creating a save state, then returning to the game, takes a long time. In particular, playing Pokemon RomHacks, I want to create a save state before the battle. But in the middle of the battle, it's often convenient to create another save state, such as when using a risky move (don't judge me). Creating a quick save is extremely fast, but it would overwrite my save from before the battle. Quick save stacks change that.

Testing

• iPhone 15 Pro, iOS 18.0
• iPhone X, iOS 15.7.4

Checklist

General (All PRs)

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I've tested my changes with different device + OS version configurations

Experimental Feature-specific

• Added property to ExperimentalFeatures struct annotated with @Feature
• Uses @Option's to persist all feature-related data
• Locked all behavior changes behind ExperimentalFeatures.shared.[feature].isEnabled runtime check
• Isolates changes to separate files as much as possible (e.g. via Swift extensions) I added a new method to SettingsViewController. Riley, let me know if you'd prefer this in its own file. I couldn't think of a more logical hook without creating a dedicated singleton.