Nt 2587 create multi router compatible automatic page view event emission

[Lotfi Anwar L Arif (Lotfi-Arif)]

Core Auto-Page Emission

• Added shared auto-page emission logic for React Web SDK router adapters.
• Auto page events now fire on first eligible render and on route changes.
• Duplicate consecutive route keys are suppressed, including React Strict Mode double-invocation cases.
• Added payload enrichment support via pagePayload and getPagePayload, merged before calling optimization.page(...).

Router Adapters

• Introduced a tree-shakeable Next.js Pages Router adapter at @contentful/optimization-react-web/router/next-pages.
• Added NextPagesAutoPageTracker for mounting in pages/_app.tsx, with all next/router usage isolated to the adapter subpath.
• Introduced a tree-shakeable Next.js App Router adapter at @contentful/optimization-react-web/router/next-app.
• Added NextAppAutoPageTracker for mounting in a client provider/layout component, with all next/navigation usage isolated to the adapter subpath.
• Introduced a tree-shakeable React Router adapter at @contentful/optimization-react-web/router/react-router.
• Added ReactRouterAutoPageTracker for mounting once inside the react-router-dom router tree.
• Introduced a tree-shakeable TanStack Router adapter at @contentful/optimization-react-web/router/tanstack-router.
• Added TanStackRouterAutoPageTracker for mounting once inside the TanStack router tree.

Package Structure and Types

• Kept router support isolated to router-specific subpath exports so the base package entry does not import router libraries.
• Exported shared auto-page types and router adapter types/context types for all supported adapters.
• Refactored the implementation to use router package types directly where practical to keep the adapter surface simpler and easier to follow.

Testing

• Refactored the unit tests and split them into less redundant testing utils and testing cases.
• Added rstest coverage for shared emitter behavior and all four router adapters.
• Covered initial emission, route transitions, duplicate suppression, and static/dynamic payload enrichment behavior.

Docs and Dev Harness

• Updated React Web SDK docs with setup and enrichment examples for all four routers, plus tree-shakeability guidance.
• Documented that this feature is implemented through page payload composition only and does not require interceptors.
• Updated the dev harness to mount the React Router adapter so auto page emission can be exercised interactively through client-side navigation.

Verification

• Verified with typecheck, eslint, prettier, and unit tests.