_CommandChooser logic selects unwanted commands

When writing tests for core.multiplexer._CommandChooser I've noticed that the request selection defined here:

seems to work wrong in some cases, e.g.

with want_cmds=1 and want_activates=0, ACTIVATE commands will still be considered, because they have both is_write=0 and is_read=0 (and we have both want_reads=0 and want_writes=0), so read and write are true, and thus (read & write) is true, even though command is false
all want_* are 0, then both read and write are 1 for requests with request.is_cmd == 1 so the command is considered valid
with want_writes=1 and want_reads=1, both write and read commands will be considered invalid (but we never want both at the same time, so it is probably a minor problem)

This behaviour can be observed in the following tests from test_command_chooser.py that fail:

enjoy-digital / litedram