Make failed requests in Run phase progress more obvious / explicit

[daverigby]

Requests are expected to succeed - if they fail then that's something which should be highlighted to users, but it's not particulary obvious right now - only shown in the failures column in a busy table:

2024-06-21T13:20:20 INFO     Completed Run phase, took 46.08s                                                                                                                                                                                                                                                                 
2024-06-21T13:20:23 INFO         Type     Name                                                                          # reqs      # fails |    Avg     Min     Max    Med |   req/s  failures/s                                                                                                                             2024-06-21T13:20:23 INFO         --------|----------------------------------------------------------------------------|-------|-------------|-------|-------|-------|-------|--------|-----------                                                                                                                             
2024-06-21T13:20:23 INFO         Search   mnist                                                                          10000    21(0.21%) |     79       8    1960     30 |  203.78        0.43                                                                                                                             
2024-06-21T13:20:23 INFO         --------|----------------------------------------------------------------------------|-------|-------------|-------|-------|-------|-------|--------|-----------                                                                                                                             
2024-06-21T13:20:23 INFO                  Aggregated                                                                     10000    21(0.21%) |     79       8    1960     30 |  203.78        0.43                                                                                                                             

Note the "# fails" column above.

Possible improvement idead:

• We show request/s, but it would also be useful to show the failed count so far. This is expected to be zero, so highlighting non-zero is valuable.
• Requests failing due to timeout (e.g. tenacity retry limit reached) are logged in vsb.log, but this isn't printed to the user. Consider if we should promote such messages to the console (might be too noisy, but could be worth it...)