feat(abigen): support empty events

[mattsse]

Motivation

Closes #2261

support unit structs in EthEvent

decoding is just checking the signature.

Solution

PR Checklist

• Added Tests
• Added Documentation
• Updated the changelog
• Breaking changes

[FrankieIsLost]

thank you!

[FrankieIsLost]

FYI, I'm not sure if the issue is fixed yet. I pulled in the fix and tried to run forge bind on the example contract from #2261 , and now get an error that looks like the following:

error[E0433]: failed to resolve: could not find `ethers_core` in the list of imported crates
   --> src/event_emitter.rs:292:9
    |
292 |         ::ethers::contract::EthEvent,
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ could not find `ethers_core` in the list of imported crates
    |
    = note: this error originates in the derive macro `::ethers::contract::EthEvent` (in Nightly builds, run with -Z macro-backtrace for more info)

I tried running forge bind on a larger project, and get the same type of error, but only on empty events.