fix a bug in interpolation of crust1.0 model

[JingChen-Thu]

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[JingChen-Thu]

See this issue
#35

@xumi1993

[codecov]

Codecov Report

❌ Patch coverage is 75.80645% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pytomoatt/io/crustmodel.py	75.40%	15 Missing ⚠️

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Pull request overview

This PR replaces the scipy-based 3D interpolation approach with a custom 2D+1D bilinear interpolation method for the CRUST1.0 model. The change appears to address accuracy issues in the original implementation by performing separate 1D vertical interpolations at grid corners followed by horizontal bilinear interpolation.

Key Changes:

• Added two helper functions (degree_to_idx and degree_to_idx_and_ratio) to convert geographic coordinates to grid indices
• Introduced a dictionary-based data structure (points_dict) that organizes model points by horizontal grid location for faster lookup
• Replaced scipy's griddata with a manual bilinear interpolation algorithm that performs 1D vertical interpolation at four corners, then blends horizontally

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[xumi1993]

I have removed old crust1.0.h5 file and added the crust1.0_points_dict.pkl to pytomoatt/data/ as dictionary. I also change the key name to (lon, lat) with tuple format. It will be easy to check bound of longitude and latitude.