MODIS: restore projection extension on new items

[DerekTan1]

Description

MODIS items created since #351 have no projection extension: no proj:wkt2, proj:transform, proj:shape or proj:geometry. #351 moved to stactools-modis 8854ceb, whose builder only reads projection from COGs passed to it. This collection attaches COGs afterwards with the deprecated add_cogs / add_cog_assets, which never set projection.

In OpenPC, every MODIS item dated mid-June 2025 onward lacks projection, as does all of modis-10A1-061, while older items still carry it. Partitions mixing the two have proj:geometry on only some rows, which stac-geoparquet cannot read.

This adds add_projection(), called right after create_item. It opens the local HDF's first subdataset once per item, as stactools-modis did before #351. Every MODIS asset shares one sinusoidal tile grid, so one read covers the item; no SAS or extra download is needed. It requests WktVersion.WKT2_2019 explicitly: the old crs.to_wkt("WKT2") passed the string as morph_to_esri_dialect, so older items stored ESRI WKT1 in proj:wkt2.

Items already created without projection need reprocessing to pick this up.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• datasets/modis/tests/test_projection.py: 2 new tests (projection fields from a GeoTIFF on the MODIS grid standing in for the HDF subdataset; error when the HDF has no subdatasets). Run from datasets/modis with python -m pytest --noconftest tests/test_projection.py.
• Applied add_projection to the live MOD10A1.A2000057.h23v07.061.2020037182526 item, using its COG in place of the HDF (local GDAL lacks HDF4). proj:transform, proj:shape and proj:geometry equal the values the item had before it was re-created, with the same CRS as real WKT2 (projection v2.0.0, proj:code: null). The item passes GeoCatalog's STAC validator.
• Every MODIS COG header (19 collections) shares one projection per item, so a single read per item is sufficient.

Note: datasets/modis/tests/test_platform_field.py imports datasets.modis.misc, which #351 deleted; it is left unchanged.

Checklist:

• I have performed a self-review
• Unit tests pass locally for the new MODIS projection tests
• Code is linted (flake8 rules, max line length 120)