Update ERC-5521: Move to Last Call

[OniReimu]

Discussion on https://ethereum-magicians.org/t/eip-5521-erc-721-referable-nft/10310.

Updated on 17 Apr: The method createdTimestampOf has been added to the interface to specifically emphasize the necessity of setting the createdTimestamp for each rNFT. This addition is not about implementation details but is a part of the specification.

Updated on 23 Apr: Fixed the grammar errors and typos.

[eip-review-bot]

✅ All reviewers have approved.

[github-actions[bot]]

The commit 3525d94b0d82b9ea214187f3302b7a4754f9e570 (as a parent of 7a5255f4a8d83d279e7ce52edb8f1ed0f1ddb630) contains errors. Please inspect the Run Summary for details.

[OniReimu]

aggreement -> agreement

Thanks for that @SamWilsn

We've fixed this and more grammar errors and typos.