fix!: identity hash is Hasher<"identity", 0>

[SgtPooki]

Breaking change because return type no longer supports sync (aligns with other hashers)

Fixes #313

[SgtPooki]

@achingbrain any qualms against this one?

[achingbrain]

With hindsight identity should be a SyncMultihashHasher.

E.g.

// identity.ts
import type { SyncMultihashHasher } from './interface.js'

// ... other code

export const identity: SyncMultihashHasher<0x00> = { code, name, encode, digest }

One problem is that identity then does not have type overlap with other Hasher instances as MultihashHasher and SyncMultihashHasher don't expose an encode property so the above will fail to compile without removing the encode prop from the export.

One (breaking) solution would be remove the encode prop above and also change the return type of from to use the MultihashHasher interface instead of the Hasher concrete implementation.

Alternatively (non-breaking) we can add the encode sig to MultihashHasher and SyncMultihashHasher though it doesn't make much sense for it to be there.