Add support for Equidistant Cylindrical ellipsoidal method (EPSG:1028)

[phaarnes]

Summary

This adds correct support for the ellipsoidal Equidistant Cylindrical while preserving the existing spherical method (EPSG:1029).

• ✅ Closes Make PROJ support the ellipsoidal Equidistant Cylindrical method (EPSG:1028) #4655 and PROJ produces incorrect Y-coordinate for EPSG:4087 (World Equidistant Cylindrical) #4654
• ✅ Tests added

What changed

• Update +proj=eqc implementation to use EPSG:1028 ellipsoidal formulas when an ellipsoid is in use, and keep the spherical implementation.
• Fixes accuracy mismatches for CRSs that use ellipsoidal EQC (e.g. EPSG:4087, IGNF:GEOPORTALFXX).
• Add/update tests for EQC and adjust IGNF CLI test expected values.
• Update EQC documentation to explicitly describe both EPSG:1028 and EPSG:1029.

Notes

Link to these two methods in EPSG:

• Equidistant Cylindrical (ellipsoidal) (EPSG;1028)
• Equidistant Cylindrical (Spherical) (EPSG:1029)

[rouault]

Thanks for this high quality contribution!