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/StateChecksum.cpp

@@ -0,0 +1,61 @@
+#include "StateChecksum.h"
+
+#include <sstream>
+
+void Hasher::appendBytes(const void* data, std::size_t byteCount)
+{
+    const unsigned char* bytes = static_cast<const unsigned char*>(data);
+    for (std::size_t i = 0; i < byteCount; ++i)
+    {
+        m_state ^= bytes[i];
+        m_state *= 1099511628211ull;  // FNV-1a 64-bit prime
+    }
+}
+
+void Hasher::append(float value)
+{
+    // Normalize -0.0f to +0.0f so the two equal values share a fingerprint.
+    if (value == 0.0f) { value = 0.0f; }
+    appendBytes(&value, sizeof(value));
+}
+
+void Hasher::append(double value)
+{
+    if (value == 0.0) { value = 0.0; }
+    appendBytes(&value, sizeof(value));
+}
+
+void Hasher::append(const QPoint& point)
+{
+    const int coords[2] = { point.x(), point.y() };
+    appendBytes(coords, sizeof(coords));
+}
+
+void Hasher::append(const QPointF& point)
+{
+    append(point.x());
+    append(point.y());
+}
+
+void Hasher::append(const QVector2D& vector)
+{
+    append(vector.x());
+    append(vector.y());
+}
+
+void Hasher::append(const std::string& text)
+{
+    appendBytes(text.data(), text.size());
+    // Length terminator so "ab"+"c" and "a"+"bc" do not collide.
+    const std::size_t length = text.size();
+    appendBytes(&length, sizeof(length));
+}
+
+std::uint64_t fingerprintRng(const std::mt19937& rng)
+{
+    std::ostringstream stream;
+    stream << rng;  // full internal state as space-separated integers
+    Hasher hasher;
+    hasher.append(stream.str());
+    return hasher.value();
+}