fix(test): feature detection for IntersectionObserver

[mfranzke]

Proposed changes

Resolves #4370

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (fix on existing components or architectural decisions)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Further comments

[github-actions]

🔭🐙🐈 Test this branch here: https://db-ux-design-system.github.io/core-web/review/4370-tooltip-can-not-be-rendered-in-test-with-react-testing-library

[Copilot]

Pull Request Overview

This PR fixes feature detection for IntersectionObserver in several UI components to ensure that the observer is only instantiated in environments where it is available.

• Added runtime checks for IntersectionObserver in tooltip, popover, and custom-select components.
• Ensured that observer initialization is conditioned on window availability and presence of IntersectionObserver.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
packages/components/src/components/tooltip/tooltip.lite.tsx	Added feature detection block for IntersectionObserver.
packages/components/src/components/popover/popover.lite.tsx	Added feature detection block for IntersectionObserver.
packages/components/src/components/custom-select/custom-select.lite.tsx	Added feature detection block for IntersectionObserver.

Comments suppressed due to low confidence (2)

packages/components/src/components/tooltip/tooltip.lite.tsx:120

• Consider adding cleanup logic to disconnect the observer when the component unmounts to prevent potential memory leaks if this is not already handled elsewhere.

if (typeof window !== 'undefined' && 'IntersectionObserver' in window) {

packages/components/src/components/popover/popover.lite.tsx:133

• Ensure that the observer is properly disconnected during cleanup to avoid any lingering observers after the component unmounts.

if (typeof window !== 'undefined' && 'IntersectionObserver' in window) {