Publish Cashu Mint and Burn Events

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This NIP proposes the introduction of three new event kinds to the Nostr protocol to facilitate the announcement of cashu mint and burn events, cashu mints identities, and the mints' outstanding balance at the end of an epoch.

The proposed event kinds aim to enhance the transparency of cashu mint and burn operations, while also providing cashu wallets with a way of querying data of interest without compromising their privacy.