Migrate remaining unit-operation state handling to StateLayout

[bernalde]

Parent: #118

Depends on the StateLayout infrastructure sub-issue and should be split into focused pull requests.

Scope

Adopt the shared layout in SolidLiquidSep, Containers, Reactors, Crystallizers, Distillation, and DynamicExtraction.

Acceptance criteria

• Migrate one coherent unit-operation family per pull request.
• Replace repeated positional packing and slicing with layout-based access.
• Add targeted regression coverage for every migrated family.
• Demonstrate unchanged numerical results apart from separately tracked defects.