litep2p: Provide partial results to speedup GetRecord queries (#7099)

This PR provides the partial results of the `GetRecord` kademlia query.

This significantly improves the authority discovery records, from ~37
minutes to ~2/3 minutes.
In contrast, libp2p discovers authority records in around ~10 minutes. 

The authority discovery was slow because litep2p provided the records
only after the Kademlia query was completed. A normal Kademlia query
completes in around 40 seconds to a few minutes.
In this PR, partial records are provided as soon as they are discovered
from the network.

### Testing Done

Started a node in Kusama with `--validator` and litep2p backend.
The node discovered 996/1000 authority records in ~ 1 minute 45 seconds.

![Screenshot 2025-01-09 at 12 26
08](https://github.com/user-attachments/assets/b618bf7c-2bba-43a0-a021-4047e854c075)


### Before & After

In this image, on the left side is libp2p, in the middle litep2p without
this PR, on the right litep2p with this PR

![Screenshot 2025-01-07 at 17 57
56](https://github.com/user-attachments/assets/a8d467f7-8dc7-461c-bcff-163b94d01ae8)



Closes: https://github.com/paritytech/polkadot-sdk/issues/7077

cc @paritytech/networking

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Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>