Harmonize reduce etas generalize df fit

[C1587S]

This PR adds geography-level aggregation support to MainRecipe, enabling damage calculations at different regional levels while maintaining backward compatibility

Changes

New parameters in MainRecipe.__init__:

• geography: One of "ir" (impact region), "country", or "globe" (default)
• country_mapping_path: Path to CSV mapping regions to countries (required for country aggregation)
• individual_region: Optional filter for single-region calculations

New methods:

• _aggregate_by_geography(): Internal helper for geography aggregation
• _aggregate_to_country(): Helper for country-level aggregation
• damages_dataset(): Returns damages as xr.Dataset with geography support
• _filter_illegal_combinations_xr(): Xarray version of illegal combination filtering
• _damage_function_points_pandas(): Original pandas-based implementation
• _damage_function_points_xarray(): New xarray-based implementation

Dual-path execution:

• When geography="globe" (default): uses original pandas path
• When geography is "ir" or "country": uses new xarray path
• Both paths return pd.DataFrame at the API boundary

Backward compatibility

• Default geography="globe" preserves existing behavior
• global_damages_calculation() returns pd.DataFrame (unchanged)
• damage_function_points returns pd.DataFrame (unchanged)
• All 238 existing tests pass without modification

Related PRs

• Builds on PR Input damages eta dimension #417 (reduce_etas) -> starting point
• Incorporates additions from PR merge "generalize DF fit" into "reduce etas"  #460 (generalize_df_fit)

Current status

• All existing tests pass (238 passed, 5 skipped)
• New geography tests verify aggregation logic
• Pandas vs xarray path equivalence verified for globe geography
• Return type consistency verified

[codecov]

Codecov Report

❌ Patch coverage is 77.63158% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.07%. Comparing base (49eda98) to head (31010aa).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/dscim/menu/main_recipe.py	71.92%	16 Missing ⚠️
src/dscim/preprocessing/preprocessing.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #476      +/-   ##
==========================================
+ Coverage   68.94%   69.07%   +0.12%     
==========================================
  Files          15       15              
  Lines        1755     1814      +59     
==========================================
+ Hits         1210     1253      +43     
- Misses        545      561      +16     

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