Attach sector demand after spatial clustering

[danielelerede-oet]

This PR moves sector demand attachment after spatial clustering, reducing the volume of demand time series processed by simplify_network and cluster_network in sector-coupled workflows (for the full US network, on the same machine, the simplify_network step reduces its runtime from ~5 hours to ~1 hour).

The PR builds on the improve_workflow branch (see #785 ).

The applied changes (limited to the defer_sector_demand branch only):

• Attach only electricity demand before network simplification and clustering.
• Store sector demand as compact zonal profiles, original bus allocation factors, growth factors, and unit conversions.
• Preserve bus mappings through simplification and clustering.
• Reconstruct sector demand in bounded blocks and aggregate it onto clustered buses, retaining original bus-level rounding.
• Replace initial electricity loads with sector loads at the start of add_extra_components, before demand response and subsequent processing.
• Update existing workflow dependencies without introducing an optional mode or configuration flag.

Note that cluster assignments may change: clustering weights now reflect electricity demand rather than all sector demands. Consequently, identical clusters or optimization results are not guaranteed.

Checklist

• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in all of config.default.yaml.
• Changes in configuration options are also documented in doc/configtables/*.csv.