Add decorator to profile unit subpub methods, added to GenAxisArray

[cboulay]

This adds a new .util.profile submodule with a decorator that can be used on a Unit's sub-pub methods.

I'm not very good at decorators, especially when using generators and asyncio together, so this will definitely need another look.

[cboulay]

Adding some details (docs will need to be added after we settle on implementation details):

• Only active when environment variable EZMSG_LOGLEVEL is set to DEBUG.
• Will log to ~/.ezmsg/profile/ezprofiler.log unless a filename is specified in environment variable EZMSG_PROFILE.
• The log file is a CSV with a header line for column titles: Source,Topic,SampleTime,PerfCounter,Elapsed
  • Source -- the module name
  • Topic -- the topic name WITHOUT the stream name (i.e., no OUTPUT_SIGNAL or INPUT_SIGNAL)
  • SampleTime -- the timestamp associated with the first (default) or the last sample in a chunk.
  • PerfCounter -- time.perf_counter() immediately after the node yielded its result.
  • Elapsed -- the difference between time.perf_counter() before the node received its data and after it yielded its result.

Some notes:

The reason for tracking SampleTime and PerfCounter (rather than just Elapsed) is so we can track a specific sample of data through a pipeline and its accumulated processing. It is not enough to look only at the Elapsed values because we might have units that yield more than 1 result per input (e.g., Window on a particular large chunk of input data). However, I've encountered some anomalies tracking samples this way, especially when dealing with data that modify the number of samples along the time axis (e.g., Downsample and Window). I'll need to sort that out before merging.

When the SampleTime cannot be known, i.e. because the method is not yielding AxisArray messages, the SampleTime is None.

I think I should add a datetime to each line.

BTW, I'm working on a live dashboard to monitor performance of a running pipeline, at least for nodes that are decorated.