feat(spv): verify the chain identity of a server on connect

After the handshake the wallet checks server.features genesis_hash and,
when the profile has checkpoints, the header at the highest checkpoint
not above the server's tip (mainnet shares Bitcoin's genesis, so the
checkpoint is what tells the chains apart). A server on another chain is
refused with WrongChainException and the next candidate is tried. Used by
the GUI, peer discovery, the CLI and the server probe. See ADR 0036.

tests/PalladiumWallet.ServerProbe/Program.cs

@@ -101,13 +101,17 @@ async Task<(bool Ok, int? Height)> Probe((string Host, int Port, bool Ssl) s)
             var r = await c.RequestAsync("server.features", ct);
             var genesis = r.TryGetProperty("genesis_hash", out var g) ? g.GetString() : null;
             var hashFn = r.TryGetProperty("hash_function", out var hf) ? hf.GetString() : null;
-            if (genesis != profile.GenesisHash)
-                throw new Exception($"genesis_hash {genesis} != expected {profile.GenesisHash} (wrong chain)");
             if (hashFn != "sha256") throw new Exception($"hash_function '{hashFn}' (expected sha256)");
             var pruning = r.TryGetProperty("pruning", out var pr) && pr.ValueKind == JsonValueKind.Number;
             return (0, $"genesis ok, pruning={(pruning ? pr.ToString() : "none")}", pruning);
         });
 
+        await Step("chain identity", async ct =>
+        {
+            await c.VerifyChainAsync(profile, ct);
+            return (0, "genesis and checkpoint match the profile", false);
+        });
+
         var tipInfo = await Step("headers.subscribe", async ct =>
         {
             var r = await c.RequestAsync("blockchain.headers.subscribe", ct);