add `--evaluator` option to `eval` command

[aanderse]

in some situations it would be beneficial to use the streaming evaluator when running colmena eval

i have a scenario where i eval something like nodes.*.config.system.build.toplevel and this takes a very long time, but running colmena apply --evaluator streaming executes in under a minute

my assumption is that colmena eval --evaluator streaming would speed things up for me