Check if ZMQ connections and queues affect memory consumption

As of now we limit ZMQ message queues, but this limit is per-connection (there is a queue for every connection)

Acceptance criteria:

• create tests (can be without Plenum, just isolated one based on ZMQ) emulating SDK client load more than server can process
  • for example 40 requests per sec from client, and 20 reads per sec by listener
  • client need to create a new connection for every 5 requests
  • create tests for Python and C implementation of ZMQ
• compare memory consumption
  • compare Python and C
  • analyse how ZMQ deals with a lot of connection (how it reads requests, and releases queues for each connections)
  • check if and when memory is released once load is stopped.
• check how Monitor affect memory consumption

Compare memory usage in each case