Build tracer-aware inputs and a linked-state CO2/O2 RHIME model

[brendan-m-murphy]

Goal

Extend multi-sector RHIME to linked primary-species/tracer inversions using shared sector states and
tracer-specific sensitivities.

Tasks

• Prepare canonical inputs with explicit species/tracer and sector structure.
• Create each sector latent once when the science requires shared degrees of freedom.
• Map sector latents into tracer-specific mu contributions through sensitivity matrices and
  conversion factors.
• Add tracer-specific total modelled observations.
• Add tracer-specific likelihoods, errors, offsets, and boundary-condition handling where needed.

Acceptance criteria

• A synthetic CO2/O2 fixture samples successfully.
• One sector latent appears once but contributes to both CO2 and O2 modelled-observation vectors.
• Latent dimensionality is lower than independent CO2 and O2 sector inversions.