Update Zarr metadata refresh to include generated filename variable

[Copilot]

update_metadata skipped filename for Zarr datasets when filename was auto-generated at write time but absent from config schema/add_variables. This left stale or missing attrs in .zattrs for that variable.

• Root cause

  • Metadata refresh iterates only over config-derived schema (full_schema).
  • For datasets like satellite_austemp_dhd_14day, filename exists in store but is not represented in config schema, so it is never updated.

• Behavior change

  • In update_store_varattrs_from_schema, when filename exists in the Zarr store but is missing from the schema input, inject a schema entry before attr reconciliation.
  • Schema source precedence:
    1. schema_transformation.add_variables.filename.schema
    2. schema.filename
    3. fallback: {type: "object", units: "1", long_name: "Filename of the source file"}

• Targeted test coverage

  • Added a unit test that removes filename from config schema/add_variables, creates a store with filename, runs metadata update, and verifies filename attrs are updated from fallback metadata.

if "filename" in store and "filename" not in schema_to_apply:
    filename_schema = (
        self.dataset_config.get("schema_transformation", {})
        .get("add_variables", {})
        .get("filename", {})
        .get("schema")
    ) or self.dataset_config.get("schema", {}).get("filename") or {
        "type": "object",
        "units": "1",
        "long_name": "Filename of the source file",
    }
    schema_to_apply["filename"] = filename_schema