Fix deprecation in erc20-counter

[Wollac]

The erc20-counter example currently dynamically creates either a block or a beacon commitment depending on its command line arguments. This uses the deprecated into_beacon_input:

// Finally, construct the input from the environment.
let evm_input = if let Some(beacon_api_url) = args.beacon_api_url {
    #[allow(deprecated)]
    env.into_beacon_input(beacon_api_url).await?
} else {
    env.into_input().await?
};

Instead, the intended behaviour in steel v1.1 is to use builder.beacon_api(url). However, as we are using a typed builder pattern, the following will not work as the type of the builder changes:

if let Some(beacon_api_url) = args.beacon_api_url { {
    builder = builder.beacon_api(beacon_api_url);
}

[linear]

WEB3-174 Fix deprecation in `erc20-counter`

[mahmudsudo]

can i take on this issue ?

[nategraf]

@mahmudsudo, sure! This is a good first issue