docs: update cloudflare kv store mention

[priley86]

Description

Updates ai-cloudflare CloudflareKVStore reference in the README to be most current.

relates to:
auth0-lab/cloudflare-agents-starter#9
auth0/docs-v2#309

References

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• GitHub Issue/PR number addressed or fixed
• Auth0 Community post
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Testing

Describe how this can be tested by reviewers. Be specific about anything not tested and reasons why. If this library has unit and/or integration testing, tests should be added for new functionality and existing tests should complete without errors.

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• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not the default branch