Duplicate storage iterator items using lightclient

Hi there,

This issue is a follow up of #1722

Fetching storage items through an iterator returns duplicates when using lightclient, hanging the loop forever with the current version of subxt. The behaviour is improved using the latest smoldot dependencies but there are still duplicates.

This isue can be confirmed when running the example below:

#![allow(missing_docs)]
use subxt::{client::OnlineClient, lightclient::LightClient, PolkadotConfig};
use std::collections::BTreeMap;

// Generate an interface that we can use from the node's metadata.
#[subxt::subxt(runtime_metadata_path = "../artifacts/polkadot_metadata_full.scale")]
pub mod polkadot {}

const POLKADOT_SPEC: &str = include_str!("../../artifacts/demo_chain_specs/polkadot.json");

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // The lightclient logs are informative:
    tracing_subscriber::fmt::init();

    let (_, polkadot_rpc) = LightClient::relay_chain(POLKADOT_SPEC)?;
    
    // Create Subxt clients from these Smoldot backed RPC clients.
    let api = OnlineClient::<PolkadotConfig>::from_rpc_client(polkadot_rpc).await?;

    let address = polkadot::storage()
        .bounties()
        .bounties_iter();

    let mut iter = api.storage().at_latest().await?.iter(address).await?;

    let mut data = BTreeMap::new();
    while let Some(Ok(storage)) = iter.next().await {
        let id = get_bounty_id_from_storage_key(storage.key_bytes);
        data.entry(id).and_modify(|n| *n += 1).or_insert(1);
        assert_eq!(data.len() as u32, data.iter().map(|(_, v)| v).sum::<u32>());
    }
    
    Ok(())
}

pub fn get_bounty_id_from_storage_key(key: Vec<u8>) -> u32 {
    let s = &key[key.len() - 4..];
    let v: [u8; 4] = s.try_into().expect("slice with incorrect length");
    u32::from_le_bytes(v)
}

Reproduce the issue with the Rust example in the report, focusing on the lightclient-backed storage iterator and its interaction with the smoldot dependencies. Trace the iterator behavior and compare results with the updated dependencies; done means storage iteration no longer yields duplicate items and the loop terminates normally.