Respect STAC cube:dimensions as source of truth in metadata_from_stac + align tests with dimension policy

[suriyahgit]

Problem

metadata_from_stac() previously injected openEO default dimensions (x, y, t, bands) even when a STAC object already defined dimensions via cube:dimensions.

This led to:

• dimension names being overridden or altered,
• inconsistencies between STAC metadata and openEO metadata,
• tests relying on implicit default behavior instead of STAC semantics.

Fix

Introduce a clear dimension resolution policy:

• If cube:dimensions is present
  → treat it as the source of truth and preserve dimension names and order.

• If cube:dimensions is absent
  → fall back to openEO defaults (x, y, optional t).

The metadata parsing logic was refactored accordingly and aligned with PySTAC datacube capabilities.

Testing

• Updated existing tests to no longer assume an always-present band dimension.

• Added checks verifying:

  • fallback behavior when cube:dimensions is missing,
  • preservation of dimension names when cube:dimensions exists,
  • correct temporal dimension handling across STAC object types.

• Tests now explicitly enforce the new dimension policy to prevent regressions.

This change makes metadata parsing more STAC-compliant while keeping backward-compatible fallback behavior.

Refer:
https://github.com/destine-datalake-cube/dedl-openeo-coordination/issues/3
Also solves: #743

[soxofaan]

just could give this a quick scan to make some notes

[suriyahgit]

ready for review @soxofaan

[clausmichele]

Hi @soxofaan , please let us know if there is something we can do to move on with this PR!

[jdries]

can a STAC 1.1 style test case be added which uses the new 'bands' common metadata and no datacube extension?
Collection metadata example:
https://github.com/radiantearth/stac-spec/blob/master/examples/collection-only/collection.json#L152
Bands spec:
https://github.com/radiantearth/stac-spec/blob/master/commons/common-metadata.md#band-object

[jdries]

FYI, Stefaan is on holiday
Added one comment myself.
Please also add a changelog entry.
Otherwise I'm inclined to say it looks good, assuming this change mostly preserves existing behaviour. (Biggest worry are collections with faulty datacube extension metadata that would suddenly have a change in behavior.)