Add test for ActiveSamplingRequest

[ackintosh]

Issue Addressed

I've implemented batching sampling requests in #6256, but there are no unit tests for it yet.

Proposed Changes

Add a test for ActiveSamplingRequest to ensure that the requests are batched, and check the status of the requests.

[michaelsproul]

Please update to point at unstable by either:

1. Rebasing on unstable (if your branch has a small number of commits that are easy to tease out), or
2. Merging origin/das into this PR: git fetch origin; git merge origin/das. This will result in the smallest number of conflict resolutions and is better for branches that already contain merge commits or have extensive history.

[ackintosh]

Thanks for the comment Michael! I've rebased this on unstable.

[dapplion]

Can you write tests in this format and file?

lighthouse/beacon_node/network/src/sync/block_lookups/tests.rs

Line 2011 in 5a96687

fn custody_lookup_happy_path() {

We recently avoided adding unit tests too close to impl for event-based tests

[ackintosh]

Thanks @dapplion! I've written tests in the tests.rs file.