feat(collection): resample from_point cubes onto the exact local-UTM grid

[MAfarrag]

Context

from_point computed the local-UTM AOI square but discarded it, calling from_stac with no grid — so the returned cube
sat on the assets' native grid, not the exact edge_size×edge_size local-UTM grid the docstring promised. The code
flagged this as the "not yet" PC-2 gap, to be closed once the grid-match landed.

Problem / Current Behaviour

Point cubes are not co-registered onto the requested grid; _point_aoi_bbox throws away the UTM square it computes.

Affected locations

File	Symbol	Notes
src/pyramids/dataset/_stac.py	from_point, _point_aoi_bbox	return + use the UTM bbox
src/pyramids/dataset/collection.py	DatasetCollection.from_point	docstring

Proposed Solution

from_point builds Grid(crs=<local UTM>, resolution, bounds=<snapped UTM square>) and forwards it to from_stac, so
every timestep is resampled onto that exact grid.

Out of Scope

A user-facing grid override on from_point (the grid is derived from lat/lon/edge_size/resolution).

Effort Estimate

Size: S — depends on the Grid dataclass.

Definition of Done

• _point_aoi_bbox returns the UTM AOI square
• from_point resamples onto the exact local-UTM grid via Grid
• tests assert the forwarded Grid (crs/resolution/bounds); docstrings updated

Depends on the Grid dataclass (see the from_stac grouping issue). Implemented in PR #951.