Minor fixes for `cargo clippy` lint output · eycorsican/leaf@ac323bc

The following actions uses node12 which is deprecated and will be forced to run on node16: actions/checkout@v2. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

The following actions use a deprecated Node.js version and will be forced to run on node20: actions/checkout@v2, hecrj/setup-rust-action@v1. For more info: https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/

unused variable: `gw`

function `test_tcp_half_close_on_configs` is never used

function `file_hash` is never used

function `test_data_transfering_reliability_on_configs` is never used

function `run_tcp_echo_server` is never used

function `run_udp_echo_server` is never used

function `run_echo_servers` is never used

function `run_leaf_instances` is never used

function `new_socks_outbound` is never used

function `new_socks_stream` is never used

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