API for LightClientBootstrap, LightClientFinalityUpdate, LightClientOptimisticUpdate and light client events

[GeemoCandama]

Issue Addressed

#4894 and partially #3651

Proposed Changes

This PR implements the following Beacon APIs:

• new: /eth/v1/beacon/light_client/bootstrap/{block_root}
• new: /eth/v1/beacon/light_client/optimistic_update
• new: /eth/v1/beacon/light_client/finality_update
• updated: Add light_client_optimistic_update and light_client_finality_update topics to /eth1/v1/events.

Additional Info

When the --light_client_server is not enabled a generic 404 Not Found is returned, whereas when the server is enabled but the server has no latest update stored, a 404 with the message saying that No LightClientOptimisticUpdate is available.

[dapplion]

The routes added by this PR follow the spec at a time. It is not compliant with current spec as the types have not been updated to use the new lightclient header type.

Since all server routes are behind a flag this PR is technically a strict improvement over unstable. The types can be fixed in a follow-up PR. Left a note on the eth2 lib, which will expose a broken client available by default.

I would suggest to fix conflicts and merge as-is, and optionally delete the http client routes

[dapplion]

Impl is correct and good except two nits!

[dapplion]

Everything looks good now, excellent!

Surfacing the two CI errors for others, both appear to be unrelated?

compile-with-beta-compiler

 Compiling slot_clock v0.2.0 (/home/runner/work/lighthouse/lighthouse/common/slot_clock)
error: unused import: `std::time::SystemTimeError`
 --> common/slot_clock/src/system_time_slot_clock.rs:5:9
  |
5 | pub use std::time::SystemTimeError;
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `-D unused-imports` implied by `-D warnings`
  = help: to override `-D warnings` add `#[allow(unused_imports)]`

error: could not compile `slot_clock` (lib) due to previous error

check-code

error: unnecessary map_err on constructor Err(_)
   --> beacon_node/lighthouse_network/src/rpc/codec/ssz_snappy.rs:380:14
    |
380 |         _ => Err(err).map_err(RPCError::from),
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Err(RPCError::from(err))`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_map_on_constructor
    = note: `-D clippy::unnecessary-map-on-constructor` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::unnecessary_map_on_constructor)]`

   Compiling ethers-contract-derive v1.0.2
error: could not compile `lighthouse_network` (lib) due to previous error

[jimmygchen]

Yeah these are related to the new Rust release (fix in #4931) and new lint warnings from the new beta compiler version (fix in #4932)

[jimmygchen]

I've made a couple of changes to bring this PR up to date with unstable. I think it looks good to me now - would be good to have this merged first, as there are a few parallel work streams on light client right now (caching optimisation, capella types etc) that may depend on some of the fixes here.

[michaelsproul]

Looks great! I had one very minor perf suggestion, but sounds like we'll be re-working and optimising this anyway so happy to merge without it!

[michaelsproul]

Rad, lets merge once CI passes.