flutter3d_sim 0.4.0

The simulation: a fixed step, an ECS, levels, navigation, saves and replays. Plain Dart, so it runs on a server.

0.4.0

• First release. It is flutter3d_game's inside, moved out whole: the fixed step, the entity store, the level format and its validator, saves, demos and the rewind buffer, world logic, actors, navigation, the camera rig and the maths. Nothing changed behaviour; the imports moved and the package boundary is new.
• Plain Dart, and that is the reason it exists. A server that verifies a submitted run has to replay it through the same simulation the player ran, and a Flutter SDK in that container is a blocker rather than an inconvenience. flutter3d_game keeps the eight files that reached Flutter — the touch and keyboard widgets, the MediaQuery read, the diagnostics sink — and re-exports this package, so no existing program changes a line.
• The boundary is a check, not a comment: the simulation names no Flutter in tool/structure.dart scans lib/, test/ and bin/.
• StateDigest and DigestTrace come with it — a 32-bit digest over the bits of a snapshot, computed the same way in a browser as in the VM, and a checkpoint trace that names the first step two runs disagree at.
• dart run flutter3d_sim:bake_visibility moves here from flutter3d_game, where it had never needed Flutter either.