Add more statistics to the build command reports

The following discussion from !54 (merged) should be addressed:

• @clemenci started a discussion:

  We should could have something like the report of the time command. time (the command not the bash builtin) allows you to customize the report so we could make it print (or write to a temporary file) what we want (elapsed time, system time, user time, memory, ...), even directly as a Python dictionary:

  ❯ \time -f '{"duration": "%E", "maxresident": %M}' sleep 1
  {"duration": "0:01.00", "maxresident": 576}

  In principle we could store all the metrics that time records, but that would probably be too much. Better to store just some basic info like time, memory and average cpu.