Reduce eth2 dependency space

[macladson]

Proposed Changes

Remove certain dependencies from eth2, and feature-gate others which are only used by certain endpoints.

Removed	Optional	Dev only
either enr libp2p-identity multiaddr	protoarray eth2_keystore eip_3076 zeroize reqwest-eventsource futures futures-util	rand test_random_derive

This is done by adding an events feature which enables the events endpoint and its associated dependencies.
The lighthouse feature also enables its associated dependencies making them optional.

The networking-adjacent dependencies were removed by just having certain fields use a String instead of an explicit network type. This means the user should handle conversion at the call site instead. This is a bit spicy, but I believe PeerId, Enr and Multiaddr are easily converted to and from Strings so I think it's fine and reduces our dependency space by a lot. The alternative is to feature gate these types behind a network feature instead.

Additional Info

Here are some cargo tree stats before and after these changes:

# Before
➜ cargo tree -p eth2 --all-features -e normal | wc -l
906
➜ cargo tree -p eth2 --no-default-features -e normal | wc -l
906

# After
➜ cargo tree -p eth2 --all-features -e normal | wc -l
786
➜ cargo tree -p eth2 --no-default-features -e normal | wc -l
669

[macladson]

We could also consider feature gating all SSZ related crates/dependencies if we can. The http client would then basically be JSON-only which is probably suitable for many use cases, and might even be required for WASM support

[michaelsproul]

Looks great! Definitely a step in the right direction!

[michaelsproul]

Another thing we could do is split the "standard" VC endpoints and Lighthouse VC endpoints. At the moment both are under the same feature as lighthouse. Only the standard VC endpoints require eip_3076, for example.

[michaelsproul]

Just noting that this attribute means we will not be able to use TestRandom on BlobsBundle in any crates that depend on eth2, because dependencies do not get compiled with cfg(test):

• #[cfg(not(test))] doesn't work in dependencies rust-lang/rust#59168

This is fine at the moment, but might need to be adjusted in future. And in general I think we should be wary of putting any actual code behind cfg(test). A separate cfg(feature = "testing") is the alternative.

[michaelsproul]

I like that the git blame for this line will now be your username 😉

[mergify]

Merge Queue Status

✅ The pull request has been merged

This pull request spent 39 minutes 47 seconds in the queue, including 37 minutes 54 seconds running CI.
The checks were run on draft #8552.

Required conditions to merge

• check-success=local-testnet-success
• check-success=test-suite-success