txHandler: Use IP address instead of IP:port pair

[algorandskiy]

Summary

Make ERL more strict by distinguishing IP addresses instead of connections.
Idea (basically as suggested in this comment: #6176 (comment))

1. TxHandler how has erlClientMapper entity that maps sender's addresses to a meta peer erlIPClient.
2. ERL gets the same erlIPClient for senders (connections) with the same address and it's logic not changed.
3. erlIPClient tracks senders with the same address.
4. erlIPClient sets own OnClose handlers so that when network actually closes a connection, this handler is called.
5. When all connections closed (peers removed) the main OnClose called to notify ERL about this client termination.

Test Plan

• A new erlIPClient unit test
• ERL-counting/correctness test
• Cluster performance test results

branch	results
master	relay summary: 8263.21 TPS, 3.12s/block, tx 56.4MB/s, rx 36.4MB/s, p2p tx 0.00B/s, p2p rx 0.00B/s
feature	relay summary: 8316.12 TPS, 3.10s/block, tx 52.4MB/s, rx 33.8MB/s, p2p tx 0.00B/s, p2p rx 0.00B/s

Memory use remained the same but the test does not have thousands of clients to tell for sure.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.80%. Comparing base (1d93b27) to head (686aaed).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6176      +/-   ##
==========================================
+ Coverage   51.76%   51.80%   +0.04%     
==========================================
  Files         644      644              
  Lines       86506    86548      +42     
==========================================
+ Hits        44777    44840      +63     
+ Misses      38852    38842      -10     
+ Partials     2877     2866      -11     

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[algorandskiy]

Remerged, fixed a possible race condition in closer

not in list