feat(sol!): make #[sol(rpc)] default if rpc feat enabled

[yash-atreya]

Motivation

Currently when expanding contracts in the sol! the rpc attribute is not enabled by default. Users must explicitly enable using #[sol(rpc)].

Solution

Introduces "rpc" feature that is propagated from alloy-core to alloy-sol-macro-expander.
Enabling this feature expands the contract with RPC-related code.

Now, one can make use of ContractInstance::new(addr, provider) without having to specify #[sol(rpc)].

RPC-related methods can be disabled using #[sol(rpc = false)].

Note: Enabling this by default requires the user to install alloy-contract.

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[gakonst]

If the user has the contract feature turned off, or if they haven't installed alloy-contract, let's error / warning to prompt the user to do so

[DaniPopes]

Sorry but I disagree with this, just like with adding derives by default, this makes compilation a lot slower and it's counterintuitive to how the rest of the ecosystem works: derives are opt-in for extra functionality

The default codegen requires the minimum dependencies. RPC codegen is straight up not possible in many contexts like no_std, so this is also a breaking change.