Function registerFetchIpnsLookup

registerFetchIpnsLookup(
    fetch: Pick<
        Fetch,
        "registerLookupFunction"
        | "unregisterLookupFunction",
    >,
    lookup: LookupFunction,
): () => void
Register an IPNS record LookupFunction on the libp2p fetch service under IPNS_PREFIX. Returns a function that unregisters it.

Only register this if you are NOT using @helia/ipns's pubsub routing. That router registers its own lookup under the same /ipns/ prefix, and @libp2p/fetch rejects a second registration for a prefix outright:
```
InvalidParametersError: Fetch protocol handler for key prefix '/ipns/' already registered
```
So this is for nodes serving IPNS over fetch without that router, not an addition to it.
Parameters
- fetch: Pick<Fetch, "registerLookupFunction" | "unregisterLookupFunction">
- lookup: LookupFunction
Returns () => void
- Defined in src/libp2p-fetch/ipns.ts:83