agreement: update AttachReceivedAt to handle compound (PP) messages

[cce]

Summary

PP messages in the first period are compound messages, containing both a vote and a proposal, which are converted into a special messageEvent by setupCompoundMessage() with a structure like this:

messageEvent{
    T: votePresent, 
    Input: voteMsg, 
    Tail: &messageEvent{
        T: payloadPresent, 
        Input: proposalMsg}}

In TestPlayerRetainsReceivedValidatedAt in #5041 I was only testing sending in two separate vote and proposal messageEvents, not a single compound messageEvent like this, and so I missed this important case when attaching receivedAt timings.

Test Plan

• update TestPlayerRetainsReceivedValidatedAt to handle this compound message case.
• add back additional test exercising separate messageEvents too, as was tested before.
• add some additional player tests that send in messageEvents with non-nil Tail fields for additional coverage Will do this in separate PR — requires updating the rest of player_test.go
• update testing helper function getTrace().Contains(ev) to do a more thorough job comparing all the fields of expected events/actions against the trace, instead of just the action type. This would have helped me catch this more quickly (for example complaining that the verifyVote action's TaskIndex was not the same as the expected value I was passing into Contains()) Would require updating other player_test.go tests that rely on the current getTrace().Contains() behavior, will do in separate PR

[codecov]

Codecov Report

Merging #5142 (73b28b4) into master (02af4ca) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #5142   +/-   ##
=======================================
  Coverage   53.45%   53.46%           
=======================================
  Files         431      431           
  Lines       54364    54368    +4     
=======================================
+ Hits        29061    29066    +5     
+ Misses      23049    23048    -1     
  Partials     2254     2254           

Impacted Files	Coverage Δ
agreement/proposal.go	71.96% <ø> (ø)
agreement/demux.go	90.68% <100.00%> (ø)
agreement/events.go	62.50% <100.00%> (+0.87%)	⬆️
ledger/tracker.go	74.26% <0.00%> (-0.85%)	⬇️
ledger/acctonline.go	78.64% <0.00%> (-0.53%)	⬇️
network/wsPeer.go	67.81% <0.00%> (-0.46%)	⬇️
ledger/testing/randomAccounts.go	56.88% <0.00%> (+0.61%)	⬆️
catchup/service.go	70.11% <0.00%> (+1.17%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[algorandskiy]

I did not dig deep into assertCorrectReceivedAtSet but the new AttachReceivedAt looks safe and valid.

[iansuvak]

Read through both changes and the tests and it looks good to me.