Missing support for multi-channel counter reads in stream_readers and task

[zhindes]

Note: this is a VERY uncommon use-case. We can probably ignore this for a bit, and nobody would notice. We didn't for a long time!

DAQmx supports having multiple Counter Input channels in a single task (note: these may not be 100% correct, and I may be missing some. We'll need to do a little digging to get the full landscape of what is possible):

• 9361 supports multiple counters in a single task doing a double-datatype read, e.g. multiple duty cycle reads
• X Series supports multiple pulse counters in a single task

I suspect the channel_collection APIs handle this already. It doesn't look like task.read supports this. double probably work as-is, but pulses definitely not. And there are no stream_reader (ChannelReaderBase) classes that are appropriate. We have a CounterReader, but that should probably be CounterSingleChannelReader (with continued support using the old name and deprecation), and we don't have a CounterMulChannelReader.