feat: implement new beacon APIs(accessors for pending_deposits/pending_partial_withdrawals)

[syjn99]

Issue Addressed

Resolves #7003

Proposed Changes

Added two endpoints as ethereum/beacon-APIs#500 proposed:

• /eth/v1/beacon/states/{state_id}/pending_deposits
• /eth/v1/beacon/states/{state_id}/pending_partial_withdrawals

[michaelsproul]

Looks good at a glance, you're definitely on the right track. I've triggered CI so you can see if the tests pass. You can also run locally, just not in debug mode

[michaelsproul]

You can fix the cargo format failure by running cargo fmt --all

[syjn99]

RUST_MIN_STACK=16777216 cargo test beacon_get_state_info_electra -p http_api --test bn_http_api_tests -- --nocapture

@michaelsproul Hi, thanks to #7007, I found that my test successfully passed with the commit. However, I'm afraid that default BeaconChainHarness will always return empty list of pending_deposits/pending_partial_withdrawals as it is initialized with default value. Do I have to add a case for comparing not emptied list? If then, would you mind letting me know where the good place to start?

[michaelsproul]

I think we should include this in v7.0.0 as we have some users asking about it.

@syjn99 Do you mind rebasing your changes on the release-v7.0.0 branch? 🙏

[michaelsproul]

When you rebase, just take out all the commits from unstable (use rebase -i).

[michaelsproul]

LGTM

Just pushed one small commit to use List in the serialization rather than Vec. This saves some copying of data (List and Vec have the same serialized representation anyway, so we can mix and match them).