fix(provider): use BoxTransport in on_anvil_*

[yash-atreya]

Motivation

Currently, the on_anvil_* methods on the provider builder return a provider based on Http<Client> transport client.

Since, the default transport in Provider is BoxTransport, there exists friction when working with types that wrap a Provider. It becomes necessary to add the T: Transport generic to `Foo<P: Provider, T: Transport + Clone>>.

The following (cleaner) way isn't possible:

struct Foo<P: Provider> {
    provider: P,
}

impl<P: Provider> Foo<P> { // default transport is BoxTransport
    pub fn new(provider: P) -> Self {
        Self { provider }
    }

    pub async fn get_block_number(&self) -> TransportResult<u64> {
        self.provider.get_block_number().await
    }
}

#[tokio::main]
async fn main() -> Result<()> {
    let provider = ProviderBuilder::new().on_anvil(); // provider based on Http<Client>

    let foo = Foo::new(provider); // Won't compile

}

Solution

Box the transport after instantiating RpcClient using .boxed

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes