Bug: DynamicCollector states_di order disagrees with packed state order

[bernalde]

Parent: #118

Problem

DynamicCollector.states_di declares mass, mass_frac, temp, while the implementation packs and unpacks mass_frac, mass, temp. Manual slicing hides the mismatch and metadata-driven unpacking would silently misassign values.

Acceptance criteria

• Add a regression test comparing metadata-driven and implementation state ordering.
• Make states_di, initial packing, model unpacking, and result retrieval agree.
• Preserve numerical behavior apart from correcting the ordering contract.
• Keep this bug fix isolated from the wider StateLayout refactor.