Fix compatibility issues with TypeScript v5.5

[devjiwonchoi]

The type of LargestContentfulPaint conflicts with the new TypeScript@5.5.2, which throws an error:

error TS2687: All declarations of 'element' must have identical modifiers.
error TS2687: All declarations of 'id' must have identical modifiers.
...

The type has readonly which requires our type to be identical as well. The TypeScript:

// typescript@5.5.2/node_modules/typescript/lib/lib.dom.d.ts:14706:14

/** [MDN Reference](https://developer.mozilla.org/docs/Web/API/LargestContentfulPaint) */
interface LargestContentfulPaint extends PerformanceEntry {
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/LargestContentfulPaint/element) */
    readonly element: Element | null;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/LargestContentfulPaint/id) */
    readonly id: string;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/LargestContentfulPaint/loadTime) */
    readonly loadTime: DOMHighResTimeStamp;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/LargestContentfulPaint/renderTime) */
    readonly renderTime: DOMHighResTimeStamp;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/LargestContentfulPaint/size) */
    readonly size: number;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/LargestContentfulPaint/url) */
    readonly url: string;
    /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/LargestContentfulPaint/toJSON) */
    toJSON(): any;
}

Fixes #498

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[devjiwonchoi]

@philipwalton Sorry to ping you, this issue is a blocker of upgrading TypeScript version, would love your review for it. 🙏

[philipwalton]

This is added in v4.2.1, let me know if you're still seeing issues after upgrading.