Drop `luxon` in favor of Temporal implementation

[nikku]

What should we do?

Luxon is a heavy dependency for feelin, adding 81.6 kB (minified) to the library footprint. Temporal is an upcoming standard, implementing a similar feature set natively in the browser. Via temporal-polyfill it is available via a 20 kB library.

What we want to do is to:

• Remove luxon as a dependency
• Use temporal-polyfill which exposes the Temporal APIs
• Change our implementation to use APIs exposed by temporal

Example: Retrieve current date and time

import { Temporal } from 'temporal-polyfill'

const now = Temporal.Now.zonedDateTimeISO();

Why should we do it?

Lower bundle size, building on browser standards.

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In the future (not the first iteration) we will drop the dependency, so this library works on native APIs.