fix: use globalThis.performance in SuspenseWithPerf to avoid SSR crash

[tyler-reitz]

Fixes #328

SuspenseWithPerf was accessing the performance global directly, which throws a ReferenceError in SSR environments (e.g. Next.js) where performance is not defined as a global variable.

Replaces direct performance access with globalThis.performance, which is always safe to access. If performance is not available in the environment, it returns undefined and the optional chaining handles it gracefully — no crash.

A follow-up enhancement (tracked in #328) could have SuspenseWithPerf self-initialize Firebase Performance via useInitPerformance for richer RUM integration.

[gemini-code-assist]

Code Review

This pull request updates src/performance.tsx to safely access the performance API, preventing errors in environments where it is not globally available. The review feedback suggests simplifying this check by directly verifying typeof performance !== 'undefined' instead of checking globalThis. Additionally, it recommends replacing React.useLayoutEffect with React.useEffect inside the Fallback component to avoid SSR warnings and prevent blocking the paint.

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