feat(emulated-entrypoint): InProcessPairUp service for TK2 PvP matching

Tiny per-mode FCFS slot. First poller parks; second pairs and triggers
bridge.RegisterBattle(p1, p2, Pvp). Match cached for first poller's
next poll (consume-on-read). No MMR, no cross-mode, no timeouts --
the proper queue API is a separate spec; this is the smallest thing
that lets TK2 PvP work end-to-end.

SVSim.UnitTests/Matching/InProcessPairUpTests.cs

@@ -0,0 +1,69 @@
+using NUnit.Framework;
+using SVSim.BattleNode.Bridge;
+using SVSim.BattleNode.Sessions;
+using SVSim.EmulatedEntrypoint.Matching;
+
+namespace SVSim.UnitTests.Matching;
+
+[TestFixture]
+public class InProcessPairUpTests
+{
+    [Test]
+    public async Task TryPairAsync_on_empty_slot_returns_null_and_parks()
+    {
+        var bridge = new MatchingBridge(new InMemoryBattleSessionStore(), new BattleNodeOptions());
+        var svc = new InProcessPairUp(bridge);
+
+        var match = await svc.TryPairAsync("tk2", new BattlePlayer(1, Ctx()), CancellationToken.None);
+
+        Assert.That(match, Is.Null);
+    }
+
+    [Test]
+    public async Task TryPairAsync_with_waiting_partner_pairs_and_returns_match()
+    {
+        var bridge = new MatchingBridge(new InMemoryBattleSessionStore(), new BattleNodeOptions());
+        var svc = new InProcessPairUp(bridge);
+
+        await svc.TryPairAsync("tk2", new BattlePlayer(1, Ctx()), CancellationToken.None);
+        var match = await svc.TryPairAsync("tk2", new BattlePlayer(2, Ctx()), CancellationToken.None);
+
+        Assert.That(match, Is.Not.Null);
+        Assert.That(match!.BattleId, Is.Not.Empty);
+    }
+
+    [Test]
+    public async Task First_arrivers_next_poll_returns_cached_match_then_evicts()
+    {
+        var bridge = new MatchingBridge(new InMemoryBattleSessionStore(), new BattleNodeOptions());
+        var svc = new InProcessPairUp(bridge);
+
+        await svc.TryPairAsync("tk2", new BattlePlayer(1, Ctx()), CancellationToken.None);  // park
+        var secondPaired = await svc.TryPairAsync("tk2", new BattlePlayer(2, Ctx()), CancellationToken.None);  // pair
+        var firstCached = await svc.TryPairAsync("tk2", new BattlePlayer(1, Ctx()), CancellationToken.None);   // consume
+        var firstAgain = await svc.TryPairAsync("tk2", new BattlePlayer(1, Ctx()), CancellationToken.None);    // post-consume
+
+        Assert.That(firstCached, Is.Not.Null);
+        Assert.That(firstCached!.BattleId, Is.EqualTo(secondPaired!.BattleId));
+        Assert.That(firstAgain, Is.Null, "Consumed entry must be evicted; next call re-parks.");
+    }
+
+    [Test]
+    public async Task Different_modes_do_not_pair_across_slots()
+    {
+        var bridge = new MatchingBridge(new InMemoryBattleSessionStore(), new BattleNodeOptions());
+        var svc = new InProcessPairUp(bridge);
+
+        await svc.TryPairAsync("tk2", new BattlePlayer(1, Ctx()), CancellationToken.None);
+        var rankMatch = await svc.TryPairAsync("rank_rotation", new BattlePlayer(2, Ctx()), CancellationToken.None);
+
+        Assert.That(rankMatch, Is.Null, "Different mode shouldn't pair with tk2's waiting viewer.");
+    }
+
+    private static MatchContext Ctx() => new(
+        SelfDeckCardIds: Enumerable.Range(1, 30).Select(_ => 100_011_010L).ToList(),
+        ClassId: "1", CharaId: "1", CardMasterName: "card_master_node_10015",
+        CountryCode: "KOR", UserName: "Player", SleeveId: "3000011",
+        EmblemId: "701441011", DegreeId: "300003", FieldId: 43, IsOfficial: 0,
+        BattleType: 11);
+}