nostr: add `full` feature

[yukibtc]

By default, only std feature is enabled. Add a full feature to enable:

• std
• rand (see nostr: add rand feature and refine wasm32-unknown-* dependencies  #1167)
• os-rng (see nostr: add os-rng feature #1168)
• all-nips

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Alternatively, enable those stuff under the default features, instead of adding full feature?