Add a request pool

[DaughterOfMars]

Description of change

This PR adds a request pool to the client, which simply waits for a limited resource to arrive on a channel before calling any client request. This is implemented using an extension trait for Future which first waits for permission from the pool to make the request, then calls the original future, then returns the permission to the pool.

Links to any relevant issues

Closes #1100

Type of change

Choose a type of change, and delete any options that are not relevant.

• Bug fix (a non-breaking change which fixes an issue)
• Enhancement (a non-breaking change which adds functionality)

[thibault-martinez]

Changelog worthy

[Thoralf-M]

Just blocks forever when amount of parallel requests is > max_parallel_api_requests

Build with .with_max_parallel_api_requests(2) and then sync an account

2023-09-06 09:12:34 (UTC) iota_sdk::wallet::account::operations::syncing::addresses::output_ids::alias_foundry DEBUG [SYNC] get_alias_and_foundry_output_ids
2023-09-06 09:12:34 (UTC) reqwest::connect                           DEBUG starting new connection: https://api.testnet.shimmer.network/
2023-09-06 09:12:34 (UTC) reqwest::connect                           DEBUG starting new connection: https://api.testnet.shimmer.network/
2023-09-06 09:12:34 (UTC) iota_sdk::client::node_manager::http_client DEBUG GET: 186 ms for 200 OK https://api.testnet.shimmer.network/api/indexer/v1/outputs/basic?expirationReturnAddress=rms1qqhfjcm5gg77l9m6lmqsgr42c5drwtt9dexhpuky0kd8fhccvg8uj9k9l7h
2023-09-06 09:12:34 (UTC) iota_sdk::client::node_manager::http_client DEBUG GET: 188 ms for 200 OK https://api.testnet.shimmer.network/api/indexer/v1/outputs/basic?address=rms1qqhfjcm5gg77l9m6lmqsgr42c5drwtt9dexhpuky0kd8fhccvg8uj9k9l7h

and then nothing happens anymore (after some time the node syncing request, but syncing never continues)

Full example to reproduce

use iota_sdk::{
    client::{
        constants::SHIMMER_COIN_TYPE,
        secret::{mnemonic::MnemonicSecretManager, SecretManager},
    },
    wallet::{ClientOptions, Result, Wallet},
};

#[tokio::main]
async fn main() -> Result<()> {
    dotenvy::dotenv().ok();

    let logger_output_config = fern_logger::LoggerOutputConfigBuilder::new()
        .name("example.log")
        .target_exclusions(&["h2", "hyper", "rustls"])
        .level_filter(log::LevelFilter::Debug);
    let config = fern_logger::LoggerConfig::build()
        .with_output(logger_output_config)
        .finish();
    fern_logger::logger_init(config).unwrap();

    let client_options = ClientOptions::new()
        .with_node(&std::env::var("NODE_URL").unwrap())?
        .with_max_parallel_api_requests(2);
    let secret_manager = MnemonicSecretManager::try_from_mnemonic(iota_sdk::client::generate_mnemonic()?)?;
    let wallet = Wallet::builder()
        .with_secret_manager(SecretManager::Mnemonic(secret_manager))
        .with_client_options(client_options)
        .with_coin_type(SHIMMER_COIN_TYPE)
        .finish()
        .await?;

    let account = wallet.create_account().with_alias("Alice").finish().await?;

    println!("Syncing account");
    account.sync(None).await?;
    Ok(())
}

[Thoralf-M]

Works now, but please also add maxParallelApiRequests to the bindings ClientOptions