Test macro actions when agents stand on conveyors

[e-ndorfin]

Summary

Need test coverage for macro-action behavior when an agent itself is standing on a conveyor tile in Overcooked V3.

Context

Macro layer (overcooked_v3_macro) handles navigation, target choice, and macro completion on top of base overcooked_v3 mechanics. Conveyor systems live in jaxmarl/environments/overcooked_v3/systems/. Unclear/untested how macro planning and execution behave when a conveyor moves the agent's own position mid-macro, not just conveyor-moved items.

Scope

• Verify flood-fill navigation and target choice stay valid when an agent is displaced by a conveyor while executing a macro.
• Verify macro completion/interruption logic when conveyor movement changes the agent's position relative to its macro target.
• Check whether macro bookkeeping (progress, target tile) gets stale or desynced when base transition moves the agent via conveyor.
• Add tests to tests/overcooked_v3_macro/ (and tests/overcooked_v3/ if base agent-on-conveyor mechanics need coverage too).
• Include JIT coverage per repo convention.