docs: add changelog fragment

Assisted-by: ClaudeCode:claude-opus-5-5

Author: d-v-b

changes/356.feature.md

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+`zarr.open`, `zarr.open_array`, `zarr.open_group` and `zarr.open_consolidated` (and the corresponding `Array`, `Group`, `AsyncArray` and `AsyncGroup` class methods, and the metadata classes' `from_dict`) take an optional `context`, a `zarr.registry.Context` naming the extensions to read metadata with. Groups opened with a context read the metadata of their members, including consolidated metadata, with it, and groups created in them share it. The default, `Context.default()`, is the default registries, so reads without `context` are unchanged.