Handle getProof without storage root idx

[ftheirs]

Pathfinder encounters an error when querying the storage_root_idx results in None. This PR addresses these cases by handling the error and populating contract_proof with an empty vector instead.

---

While working with a devnet on Madara, we discovered a condition that occurs only in the initial blocks of the chain. From block 1 to block 9, the storage_root_idx query returns None, causing Pathfinder to immediately throw an error.
This error is propagated instead of being handled appropriately at the application layer, specifically in SNOS. Returning an empty vector allows us to continue with our workflow and handle this situation more gracefully.

On the other hand, the error received is not descriptive, forcing SNOS to interrupt execution. For example:

{"error":{"code":-32603,"message":"Internal error"},"id":1,"jsonrpc":"2.0"}

Steps to reproduce:

1. Clone repositories

git clone [email protected]:eqlabs/pathfinder.git
git clone [email protected]:madara-alliance/madara

2. Run Madara

cd madara
cargo run --release -- \
    --name madara \
    --base-path $(pwd)/madara-db \
    --rpc-port 9944 \
    --rpc-cors "*" \
    --rpc-external \
    --sequencer \
    --chain-config-path configs/presets/devnet.yaml \
    --feeder-gateway-enable \
    --gateway-enable \
    --gateway-external \
    --gas-price 1234 \
    --blob-gas-price 10 \
    --rpc-methods unsafe \
    --no-l1-sync

3. Start Pathfinder

cd ../pathfinder
cargo run --bin pathfinder -- \
    --network custom \
    --chain-id MADARA_DEVNET \
    --ethereum.url wss://eth-sepolia.g.alchemy.com/v2/WIUR5JUZXieEBkze6Xs3IOXWhsS840TX \
    --gateway-url http://localhost:8080/gateway \
    --feeder-gateway-url http://localhost:8080/feeder_gateway \
    --storage.state-tries archive \
    --data-directory ~/pathfinder/data \
    --http-rpc 127.0.0.1:9545

4. Retrieve a storage proof using curl from any block between 1 and 9

curl --request POST \
    --url http://127.0.0.1:9545/rpc/pathfinder/v0.1 \
    --header 'accept: application/json' \
    --header 'content-type: application/json' \
    --data '
{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "pathfinder_getProof",
  "params": [
    { "block_number": 5 }, "0x1", ["0x0"]
  ]
}
'

[whichqua]

Could you consider giving the PR a little more info and motivation?