refactor(collection): group from_stac target-grid params into a Grid dataclass

[MAfarrag]

Context

DatasetCollection.from_stac carried 14 parameters, five of which (like, crs, resolution, bounds, anchor)
describe one thing — the target output grid — with runtime-enforced invariants (like xor the trio; the trio is
all-or-nothing). Same class of too-many-arguments smell tracked for to_cog in #757 (python:S107).

Problem / Current Behaviour

The five loose kwargs bloat the signature and scatter validation inside _resolve_target_grid.

Affected locations

File	Symbol	Notes
src/pyramids/dataset/grid.py	Grid (new)	frozen dataclass + __post_init__ validation
src/pyramids/dataset/collection.py	DatasetCollection.from_stac	5 kwargs -> grid: Grid | None
src/pyramids/dataset/_stac.py	from_stac, _resolve_target_grid	take a Grid

Proposed Solution

from pyramids.dataset import Grid
DatasetCollection.from_stac(items, "B04", grid=Grid(crs=32633, resolution=10, bounds=(...)))

Drops from_stac from 14 to 10 params; mirrors odc.stac.load's geobox= grouping.

Out of Scope

from_point (tracked separately); other constructors.

Effort Estimate

Size: S — new dataclass + signature change + test migration.

Definition of Done

• Grid dataclass with mode-invariant validation, exported from pyramids.dataset
• from_stac takes grid=Grid(...) (breaking; no alias)
• tests + docs updated

Relates to #757 (same S107 parameter-count reduction). Implemented in PR #951.