Remove spectral attributes from DataArray

[ecomodeller]

Summary

Remove spectral-specific attributes from DataArray to ensure consistent API across all geometry types. Spectral information is now accessed through geometry, maintaining a clear separation of concerns.

Migration path: Deprecated properties provide backward compatibility with warnings that guide users to the new API.

Why This Change?

DataArray should have a consistent interface regardless of geometry type. Previously, DataArrays with spectral geometries had extra attributes (frequencies, directions) that weren't available for other geometry types, creating an inconsistent API.

After this change:

• ✅ All DataArrays have the same interface
• ✅ Geometry-specific information stays in geometry
• ✅ Easier to understand and maintain

Migration Guide

Accessing Spectral Metadata

Spectral information is now accessed through the geometry:

# Old (deprecated, shows warning)
freq = da.frequencies
n_freq = da.n_frequencies
dirs = da.directions
n_dirs = da.n_directions

# New - access through geometry
freq = da.geometry.frequencies
n_freq = da.geometry.n_frequencies
dirs = da.geometry.directions
n_dirs = da.geometry.n_directions

The old syntax still works but shows a FutureWarning pointing you to the new API.

Changes

What Changed

Old API	New API	Status
da.frequencies	da.geometry.frequencies	Deprecated with warning
da.n_frequencies	da.geometry.n_frequencies	Deprecated with warning
da.directions	da.geometry.directions	Deprecated with warning
da.n_directions	da.geometry.n_directions	Deprecated with warning

What Still Works

• ✅ Reading spectral files: mikeio.read("spectrum.dfsu")
• ✅ Plotting spectral data: da.plot() works unchanged
• ✅ Accessing spectral geometry: da.geometry has all spectral metadata
• ✅ All other DataArray operations

Implementation

• Added deprecated properties with FutureWarning to guide users to new API
• Properties forward to geometry so code continues to work during migration
• Moved internal Hm0 calculation to plotting module (_calc_Hm0() helper)
• Updated notebooks to use new da.geometry.frequencies pattern
• Clearly marked deprecated section in code for easy future removal