fix(examples): Hide edit button outside editor

[zJaaal]

This pull request includes changes to the examples/nextjs/src/components/shared/contentlets.js file to improve the functionality and performance of the Contentlets component. The most important changes include replacing React with useMemo, adding a new import for isInsideEditor, and conditionally rendering the edit button based on whether the contentlet is inside the editor.

Improvements to functionality:

• examples/nextjs/src/components/shared/contentlets.js: Replaced the React import with useMemo to memoize the isInsideEditor function.
• examples/nextjs/src/components/shared/contentlets.js: Added a new import for isInsideEditor from @dotcms/client to check if the contentlet is inside the editor.
• examples/nextjs/src/components/shared/contentlets.js: Used useMemo to create a memoized value insideEditor for determining if the contentlet is inside the editor.
• examples/nextjs/src/components/shared/contentlets.js: Conditionally rendered the edit button based on the insideEditor value to improve user experience.

This PR fixes: #30218