refactor: Consolidate cost loading functions

[fneum]

Closes #1449 .

Changes proposed in this Pull Request

This pull request focuses on unifying and refactoring cost-related functions across multiple scripts, as well as updating the documentation to reflect these changes. The most important changes include the consolidation of cost functions, updates to the load_costs function, and modifications to various scripts to use the new unified function.

• Unified the functions load_costs in add_electricity and prepare_costs in prepare_sector_network into a single function load_costs in add_electricity.

• Refactored the load_costs function in add_electricity.py to include detailed docstrings, parameter descriptions, and updated processing logic. [1] [2]

Checklist

• I tested my contribution locally and it works as intended.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in config/config.default.yaml.
• Changes in configuration options are documented in doc/configtables/*.csv.
• Sources of newly added data are documented in doc/data_sources.rst.
• A release note doc/release_notes.rst is added.

PR Overview

This PR refactors and consolidates cost loading functions by replacing the old prepare_costs implementation with a unified load_costs function in add_electricity.py, and updates dependent scripts accordingly. Key changes include:

• Changing the load_costs API (renaming parameters, updating logging messages, and improved unit handling)
• Replacing usages in scripts (make_summary.py, make_summary_perfect.py, add_existing_baseyear.py, prepare_sector_network.py) to import and use the new unified function
• Updating the CO2 cost assignments to use the “CO2 intensity” column consistently

Reviewed Changes

File	Description
scripts/add_electricity.py	Refactored load_costs function signature and updated CO2 column mapping
scripts/make_summary.py	Replaced prepare_costs with load_costs and adjusted parameter naming
scripts/make_summary_perfect.py	Similar updates to cost loading function and parameter names
scripts/add_existing_baseyear.py	Updated import and usage of load_costs replacing prepare_costs
scripts/prepare_sector_network.py	Removed the old prepare_costs function and updated imports

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

scripts/add_electricity.py:205

• Multiple duplicate definitions of the load_costs function appear in this file. Consider consolidating them into a single definition to avoid potential conflicts and maintenance issues.

def load_costs(cost_file: str, config: dict, max_hours: dict = None, nyears: float = 1.0) -> pd.DataFrame:

scripts/add_electricity.py:200

• The updated CO2 cost assignment now fetches values from the 'CO2 intensity' column. Please verify that this change aligns with downstream processing, ensuring all references to cost-related CO2 data are updated accordingly.

n.carriers.loc[carriers, "co2_emissions"] = costs.loc[suptechs, "CO2 intensity"].values