fix: data race in BenchmarkConnectionMainReadLoop (#1040)

_pendingPieces.Add(0) was called without holding the client lock and
without updating the piece request order, causing two issues:
1. Data race with timer goroutines accessing the roaring bitmap
2. Panic in checkPendingPiecesMatchesRequestOrder due to _pendingPieces
   and requestOrder being out of sync

Replace the direct bitmap manipulation with updatePiecePriority(0, ...)
which properly updates both _pendingPieces and the piece request order
while holding the client lock.

Co-authored-by: info@weblogix.biz <admin@10gbps.weblogix.it>
Co-authored-by: Matt Joiner <anacrolix@gmail.com>

Author: 3 people

peerconn_test.go

@@ -120,6 +120,9 @@ func BenchmarkConnectionMainReadLoop(b *testing.B) {
 	}))
 	//t.storage = &storage.Torrent{TorrentImpl: storage.TorrentImpl{Piece: ts.Piece, Close: ts.Close}}
 	//t.onSetInfo()
+	cl.lock()
+	t.updatePiecePriority(0, "benchmark setup")
+	cl.unlock()
 	r, w := net.Pipe()
 	b.Logf("pipe reader remote addr: %v", r.RemoteAddr())
 	cn := cl.newConnection(r, newConnectionOpts{