refactor(browser-sdk): refactor overrides API

[roncohen]

includes new example of how to make your own toolbar.

Screen.Recording.2025-06-04.at.13.29.10.mov

[Copilot]

Pull Request Overview

This PR refactors the overrides API for feature flags across the browser and react SDKs and introduces a new example toolbar for custom feature control.

• Refactors API methods to use setIsEnabledOverride instead of legacy setFeatureOverride/getFeatureOverride.
• Updates tests and UI components (Toolbar and FeaturesTable) accordingly to support local override changes.
• Adds a new CustomToolbar component in the react-sdk to demonstrate how to create a custom toolbar.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/react-sdk/dev/plain/app.tsx	Adds CustomToolbar import and usage in the demos section.
packages/browser-sdk/test/usage.test.ts	Updates tests to include new override API properties.
packages/browser-sdk/test/client.test.ts	Refactors tests to use getFeature(...).setIsEnabledOverride method.
packages/browser-sdk/src/toolbar/Toolbar.tsx	Replaces legacy override logic with direct use of isEnabledOverride.
packages/browser-sdk/src/toolbar/Features.tsx	Updates props and event handlers to use setIsEnabledOverride.
packages/browser-sdk/src/client.ts	Removes legacy API and adds new isEnabledOverride APIs.