test(mempool/cat): fix flaky TestTxPool_BroadcastQueue

[catconcat]

Description

Closes #1261

[rootulp]

I can't get the flake to reproduce locally before or after this change. @tropicaldog do you mind explaining why this fixes the flake?

[catconcat]

@rootulp I think the original code might lead to a race condition, where the goroutine may start consuming transactions before all of them are added. Using time.Sleep(10 * time.Millisecond) to introduce a delay is not a reliable solution imo.
The command I use to reproduce the flaky behavior is:
go test -timeout 30s -run ^TestTxPool_BroadcastQueue$ github.com/cometbft/cometbft/mempool/cat -race -count 10
Interestingly, the flaky behavior only occurs on my M2 Mac, where the test fails 50% of the time. When I tried running the same command several times on my Ubuntu 22.04 PC, no flakiness was observed.

[rootulp]

Thanks for the explanation! I'm on an M1 Mac and the test is still passing on my machine after your fix so LGTM.

[rach-id]

unable to reproduce the flake locally on Mac, but this fix looks reasonable to me. There is no need to wait to introduce the delay where we can just broadcast all the transactions before starting to consume them

[evan-forbes]

thanks @tropicaldog

[evan-forbes]

@tropicaldog we have to update this branch by merging main, perhaps you could give one of us perms to do that on your fork so we could merge this? either that, or you will have to merge main again 😅

[catconcat]

@tropicaldog we have to update this branch by merging main, perhaps you could give one of us perms to do that on your fork so we could merge this? either that, or you will have to merge main again 😅

Yeah I guess I didn't have enough permission. Anyway I will merge main now, thanks for your reviews!