feat: Update Zustand, resolve deprecated imports

[DafyddLlyr]

What does this PR do?

• Update Zustand from 4.3.8 → 4.5.4
• Resolve deprecation warning about zustand/vanilla (see below)

Motivation

• Zustand's persist middleware may be a nice way of handling our local storage capacity issues (switching to indexdb?)
• This would also allow us to rationalise up some of the logic around session storage here -

planx-new/editor.planx.uk/src/pages/Preview/Questions.tsx

Lines 100 to 112 in b484df1

	if (isUsingLocalStorage) {
	const state = getLocalFlow(id);
	if (state) resumeSession(state);
	createAnalytics(state ? "resume" : "init");
	setGotFlow(true);
	} else {
	NEW.getLocalFlow(sessionId).then((state) => {
	// session data is resumed by ./ResumePage.tsx
	createAnalytics(state ? "resume" : "init");
	setGotFlow(true);
	});
	}
	}, []);

• Seems worthwhile to get things in ship-shape before looking into this
• The warning's been bugging me for ages! 😅

[github-actions]

Removed vultr server and associated DNS entries

[DafyddLlyr]

Zustand no longer requires the use of a vanilla store outside of React components.

This means we can use the useStore() hook in React components, and useStore.getState() elsewhere consistently.

[jessicamcinchak]

Really nice simplification!