Replay: deterministic record & playback (#4)

Add deterministic record/playback for a run.

Recording captures `(seed, config hash, ordered tick-tagged commands)` and re-simulates on playback — no state snapshots. `DotaFactory.exe --replay <file>` re-plays a recorded run view-only with manual speed/pause.

Reviewed-on: #4
Co-authored-by: Malte Langkabel <malte.langkabel@gmail.com>
Co-committed-by: Malte Langkabel <malte.langkabel@gmail.com>

src/lib/sim/ReplayPlayer.h

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <cstddef>
+#include <optional>
+#include <vector>
+
+#include "ReplayReader.h"
+#include "Tick.h"
+
+class Simulation;
+
+// Drives playback of a parsed replay against a Simulation: applies each recorded
+// command at its recorded tick (through Simulation::apply) and verifies the RNG
+// checksums, reporting the first desync. Entries are consumed in file order,
+// which reproduces the exact command/tick interleaving of the original run.
+//
+// Cadence (mirrors how the run was recorded so checksums line up):
+//   player.start();                 // process tick-0 entries before the first tick
+//   each frame, for each tick to run:
+//       if (player.isFinished()) break;
+//       sim.tick();
+//       player.advanceTo(sim.currentTick());
+class ReplayPlayer
+{
+public:
+    ReplayPlayer(Simulation& simulation, std::vector<ReplayEntry> entries);
+
+    // Process all entries recorded at tick 0 (the initial checksum and any
+    // commands issued before the first tick). Call once, before the first tick.
+    void start();
+
+    // Process all entries recorded at `tick`. Call once after each sim.tick().
+    void advanceTo(Tick tick);
+
+    // True once all entries are consumed or a desync was detected.
+    bool isFinished() const;
+
+    // The tick at which the recomputed checksum first diverged, if any.
+    std::optional<Tick> getDesyncTick() const;
+
+private:
+    void processEntriesAt(Tick tick);
+
+    Simulation&              m_simulation;
+    std::vector<ReplayEntry> m_entries;
+    std::size_t              m_cursor = 0;
+    std::optional<Tick>      m_desyncTick;
+};