[core] Make some more of IPieceRequestor readonly

The consumer of this interface shouldn't be able to set the
'IsChoking' status. That's controlled purely by whether or not
the remote peer ahs sent an Unchoke message. Similarly for
SupportsFastPeer.

This is just some cleanup now that things have been migrated to
the new interface.

src/MonoTorrent.Tests/Client/StandardPickerTests.cs

@@ -52,8 +52,8 @@ class TestTorrentData : ITorrentData
         }
 
         BitField bitfield;
-        IPieceRequester peer;
-        List<IPieceRequester> peers;
+        PeerId peer;
+        List<PeerId> peers;
         PiecePicker picker;
         TestTorrentData torrentData;
 
@@ -68,7 +68,7 @@ public void Setup()
                 PieceLength = pieceLength,
                 Size = pieceLength * pieceCount
             };
-            peers = new List<IPieceRequester>();
+            peers = new List<PeerId>();
 
             picker = new StandardPicker();
             picker.Initialise (bitfield, torrentData, Enumerable.Empty<Piece> ());
@@ -162,7 +162,7 @@ public void StandardPicker_PickStandardPiece ()
 
             peers [1].IsChoking = false;
             peers [1].BitField.SetAll (true);
-            peers [1].HashedPiece (false);
+            peers [1].Peer.HashedPiece (false);
             message = picker.PickPiece (peers [1], bitfield.Clone ().Not (), peers, 1, 0, 10);
             Assert.AreEqual (2, message[0].PieceIndex);
         }

src/MonoTorrent/MonoTorrent.Client.Connections/PeerId.PieceRequester.cs

@@ -39,11 +39,11 @@ public partial class PeerId : IPieceRequester
     {
         int       IPieceRequester.AmRequestingPiecesCount { get => AmRequestingPiecesCount; set => AmRequestingPiecesCount = value; }
         List<int> IPieceRequester.IsAllowedFastPieces => IsAllowedFastPieces;
-        bool      IPieceRequester.IsChoking { get => IsChoking; set => IsChoking = value; }
+        bool      IPieceRequester.IsChoking => IsChoking;
         Stopwatch IPieceRequester.LastMessageReceived => LastMessageReceived;
         int       IPieceRequester.RepeatedHashFails => Peer.RepeatedHashFails;
         List<int> IPieceRequester.SuggestedPieces => SuggestedPieces;
-        bool      IPieceRequester.SupportsFastPeer { get => SupportsFastPeer; set => SupportsFastPeer = value; }
+        bool      IPieceRequester.SupportsFastPeer => SupportsFastPeer;
         int       IPieceRequester.TotalHashFails => Peer.TotalHashFails;
 
         void IPieceRequester.Cancel (int pieceIndex, int pieceOffset, int requestLength)

src/MonoTorrent/MonoTorrent.Client.PiecePicking/IPieceRequester.cs

@@ -34,17 +34,14 @@ namespace MonoTorrent.Client.PiecePicking
 {
     public interface IPieceRequester
     {
-        // FIXME: Make these readonly
-        bool IsChoking { get; set; }
-        bool SupportsFastPeer { get; set; }
-        // FIXME: Make these readonly
-
         int AmRequestingPiecesCount { get; set; }
         BitField BitField { get; }
         List<int> IsAllowedFastPieces { get; }
+        bool IsChoking { get; }
         Stopwatch LastMessageReceived { get; }
         int RepeatedHashFails { get; }
         List<int> SuggestedPieces { get; }
+        bool SupportsFastPeer { get; }
         int TotalHashFails { get; }
 
         void Cancel (int pieceIndex, int pieceOffset, int requestLength);