PersistedState: add remove to remove persisted state from storage

[ibilux]

This add a remove function to remove persisted state from storage like window.localstorage.removeitem for #208.

If the initialValue is set to null the PersistedState will not create a localstorage item. Ex:

const count = $state(new PersistedState("count", null));

If the PersistedState is removed the current value will be set to null. Ex:

count.remove();

[changeset-bot]

🦋 Changeset detected

Latest commit: 8d3c5af

The changes in this PR will be included in the next version bump.

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[TGlide]

Maybe lets call it reset?

[ibilux]

Maybe lets call it reset?

I think Reset means to restore the state to its initial or default value. But this (remove) is meant to remove the persisted state from local storage entirely.

[TGlide]

Why should it be potentially null? Shouldn't that be a part of T?

[ibilux]

The removeItem() method of the Storage interface sets the item to null when it's removed. So if the user chooses a null value it won't be saved to the local storage (this is just a work around).
The #current: T | undefined; is already typed as T | undefined i didn't want to use undefined and used null instead so it won't interfere with the current codebase.