WIP txHandler: do not rebroadcast to peers sent duplicate messages

[algorandskiy]

Summary

When the transaction deduplication was added it had a side effect of re-sending transactions to peers sent a message the handler has seen before. This PR fixes this.

Before dedup if A sent T, all but A get T, then, if B sent us T, noone gets T again With dedup, if A sent T, all but A get T, then, if B sent us T, noone gets T again. With this PR: if A and B sent T almost simultaneously all but A and B get T

Implementation overview:

1. txSaltedCache how stores map of seen peers for a particular message
2. CheckAndPut returns this map to to get rid additional lookups.
3. The map is later used in RelayArray to let networking know whom to skip.

Implementation Details

CheckAndPut is not more complex because it needs to update the map value even if there is a match. The original idea with fast check under a read lock is preserved but innerCheck also returns a current value and a "page" (cur/prev map) where it was found in order to update. Note innerCheck can return prev page and this also need to be considered when running an update with a write lock taken. The found && senderFound denotes a new fast path without modification underlying maps.

Note, a reference data struct (*sync.Map in this case) is crucial to have the implementation to work because of the following scenario:

1. Received txn A from N1, wrote to the cache, the the cache value (peers list) is attached to a work item txBacklogMsg (wi ) of this transaction.
2. Received txn A from N2, updated the peers list. The reference in wi is updated automatically.
3. It is time to relay, give the network the same peers list
4. Received txn A from N3, updated to the cache value (peers list)
5. The network has updated peers list with N3
6. After broadcasting received txn A from N4, updated to the cache value (peers list), but b/c it is a duplicate it would not make its path to the network.

Test Plan

Added a new unit test

Benchmarks

master

BenchmarkDigestCaches/data.digestCacheMaker/threads=1-8         	 1000000	      1575 ns/op
BenchmarkDigestCaches/data.saltedCacheMaker/threads=1-8         	  769404	      1886 ns/op
BenchmarkDigestCaches/data.digestCacheMaker/threads=4-8         	 1347638	       992.8 ns/op
BenchmarkDigestCaches/data.saltedCacheMaker/threads=4-8         	  777824	      2042 ns/op
BenchmarkDigestCaches/data.digestCacheMaker/threads=16-8        	 1248975	       984.3 ns/op
BenchmarkDigestCaches/data.saltedCacheMaker/threads=16-8        	  709402	      2234 ns/op
BenchmarkDigestCaches/data.digestCacheMaker/threads=128-8       	 1233063	       996.1 ns/op
BenchmarkDigestCaches/data.saltedCacheMaker/threads=128-8       	  619723	      2289 ns/op

feature

BenchmarkDigestCaches/data.digestCacheMaker/threads=1-8         	  978464	      1460 ns/op
BenchmarkDigestCaches/data.saltedCacheMaker/threads=1-8         	  575578	      2303 ns/op
BenchmarkDigestCaches/data.saltedCacheDupMaker/threads=1-8      	  550164	      2238 ns/op
BenchmarkDigestCaches/data.digestCacheMaker/threads=4-8         	 1395024	       877.9 ns/op
BenchmarkDigestCaches/data.saltedCacheMaker/threads=4-8         	  499202	      2773 ns/op
BenchmarkDigestCaches/data.saltedCacheDupMaker/threads=4-8      	  651159	      1883 ns/op
BenchmarkDigestCaches/data.digestCacheMaker/threads=16-8        	 1308243	       948.8 ns/op
BenchmarkDigestCaches/data.saltedCacheMaker/threads=16-8        	  430381	      3130 ns/op
BenchmarkDigestCaches/data.saltedCacheDupMaker/threads=16-8     	  954093	      1338 ns/op
BenchmarkDigestCaches/data.digestCacheMaker/threads=128-8       	 1305469	       952.8 ns/op
BenchmarkDigestCaches/data.saltedCacheMaker/threads=128-8       	  443257	      3026 ns/op
BenchmarkDigestCaches/data.saltedCacheDupMaker/threads=128-8    	 1756513	       686.5 ns/op