Support additional DEM raster formats (NetCDF, etc.)

[mmacferrin]

Overview

IVERT currently assumes DEM inputs are GeoTIFF (.tif) files. We should extend support to NetCDF and other common raster formats so users are not required to convert their data beforehand.

Formats to Support

• NetCDF (.nc, .nc4) — widely used in oceanography and climate science
• HDF5 (.h5, .hdf5) — already used internally for ICESat-2 data; some DEMs are distributed in this format
• ERDAS Imagine (.img)
• ASCII Grid (.asc)
• VRT (GDAL virtual rasters)
• Any other GDAL-readable raster format

Tasks

• Audit input-handling code to identify all places where .tif is assumed or hardcoded
• Replace format-specific logic with GDAL-generic raster reading
• Handle multi-variable NetCDF files (allow user to specify which variable/band to use as the elevation layer)
• Update file type validation and error messaging
• Test with representative NetCDF and other non-GeoTIFF DEMs
• Update documentation and CLI help text to reflect supported formats