Gloas add spans for deposit signature verification

[eserilev]

Issue Addressed

We want to be able to measure the time it takes to sig verify deposits. We'll probably have to make optimizations to this code path (maybe a pre-processing cache?) so it'll be nice to have metrics we can look at.

• lh_process_deposit_requests_post_gloas — total time for all deposits in the block
• lh_is_pending_validator — sig verification per validator deposit
• lh_apply_deposit_for_builder — sig verification for builder deposit

[jimmygchen]

Might be worth adding count = deposit_requests.len()?

[jimmygchen]

The lh_ prefix are for top level root span only. These three spans should appear in all the block processing code paths without it.

The only uninstrumented code path I've found is when it's called from the state_advance_timer:

lighthouse/beacon_node/beacon_chain/src/state_advance_timer.rs

Line 215 in cf3d5e2

.prepare_beacon_proposer(current_slot)

[eserilev]

ah right, thanks

[jimmygchen]

A bit of context on the lh_ prefix: the main purpose is to only export spans that belongs to code paths that are instrumented end-to-end, so we don't end up with lots of individual spans appearing on uninstrumented code paths that we're less interested in.

If we prefix all spans, then it defeats the purpose of this filtering, so we should only the prefix on the top level span.

#8647

[eserilev]

pawan is handling this in his deposit Pr