Differentiate nuclear technologies by size and reactor type

I'd like to suggest the representation of nuclear power technologies by differentiating them by size (large reactors vs small modular reactors) and by reactor type (PWR, HTGR, etc.), and applying this distinction to both existing and buildable capacity.

Right now, nuclear is modeled as a single generic technology, but there are major differences between different technologies.
Each class has distinct:

• Capital cost (CAPEX);
• O&M cost structure;
• Construction time and modularity;
• Ramp rates and flexibility;
• Applicability (grid baseload vs remote/off-grid, industrial heat, etc.).

A first-level split could distinguish:

• nuclear_large
• nuclear_smr
  A second-level refinement could add specific reactor types:
• nuclear_smr_pwr
• nuclear_smr_htgr

This would better reflect current technology trends and allow more detailed modeling of future scenarios – especially given the increasing focus on SMRs in Europe, USA and beyond.

No files, tests, or entry points are named. Start by inspecting how the repository currently represents nuclear technology and existing versus buildable capacity, then review the data conventions for costs, lifetimes, construction times, and operational parameters. Done means the proposed size and reactor-type distinctions are represented consistently for both capacity categories with validated assumptions.