chore: improve styles watch performance

[gfellerph]

Only copies changed files to dist. This will improve performance for development massively because vite reacted to every change in dist individually and before, every single sass file was copied to dist regardless if it changed or not. Also, map-icons creates a theoretical infinite loop and calling watch again is not necessary within the watch task.

[changeset-bot]

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Latest commit: 97758c9

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[swisspost-bot]

Preview environment ready: https://preview-1841--swisspost-web-frontend.netlify.app
Preview environment ready: https://preview-1841--swisspost-design-system-next-v7.netlify.app
Preview environment ready: https://preview-1841--swisspost-design-system-next.netlify.app

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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1.4% Duplication