This change makes `mjtSize` a signed, rather than unsigned 64-bit integer. While sizes are non-negative, the type promotion rules for unsigned integers can lead to unituitive downstream bugs, and 8 billion terabytes are enough bytes.
PiperOrigin-RevId: 834292964
Change-Id: Iea9c47c2a5d80fde63851a543d59ed0549db0f01
Yuval Tassa
86a77ff8eb