fix(clerk-js): Use the issued at timestamp from JWT for the MemoryTokenCache

[octoper]

Description

This PR changes the createdAt value when storing a token to the MemoryTokenCache from the current user time to the issued at time of the token to check how much time has elapsed from when the token has been issued.

Checklist

• npm test runs as expected.
• npm run build runs as expected.
• (If applicable) JSDoc comments have been added or updated for any package exports
• (If applicable) Documentation has been updated

Type of change

• 🐛 Bug fix
• 🌟 New feature
• 🔨 Breaking change
• 📖 Refactoring / dependency upgrade / documentation
• other:

Packages affected

• @clerk/clerk-js
• @clerk/clerk-react
• @clerk/nextjs
• @clerk/remix
• @clerk/types
• @clerk/themes
• @clerk/localizations
• @clerk/clerk-expo
• @clerk/backend
• @clerk/clerk-sdk-node
• @clerk/shared
• @clerk/fastify
• @clerk/chrome-extension
• gatsby-plugin-clerk
• build/tooling/chore

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Latest commit: 91c35c6

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[dimkl]

❓ What issue this change will resolve?
Also i think that using the issuedAt instead of the end-user clock will not work for end-user with a clockSkew. The current implementation keeps the creation DateTime of the token based on the end-user clock and the expiration duration from the token using expiresAt - issuedAt to calculate the exact time the token will expire based on the end-user clock.
Example:
End-user A with clockSkew 10 minutes (compared to the FAPI server), retrieves token with issuedAt at 00:10:00 that will expire in 60 seconds 00:11:00 and the end-user clock is 00:00:00. After 5 seconds Frontend code executes getToken() and tokenCache.get() is executed. The code in packages/clerk-js/src/core/tokenCache.ts will be executed in the end-user with :

    const nowSeconds = Math.floor(Date.now() / 1000);  // "00:00:05"
    const elapsedSeconds = nowSeconds - value.createdAt!; // "00:00:05" - "00:10:00"
     const expiresSoon = value.expiresIn! - elapsedSeconds < (leeway || 1) + SYNC_LEEWAY; // 60 - 595 < 10 - 5   

[clerk-cookie]

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