Latest version of the package expects a `@language` tag to be in the `@context`

[amercader]

After changes introduced in #932 creating a Dataset object will fail if the @context provided doesn't have a @language tag:

Minimal example:

{
    "@context": {
        "@vocab": "https://schema.org/",
        "citeAs": "cr:citeAs",
        "column": "cr:column",
        "conformsTo": "dct:conformsTo",
        "cr": "http://mlcommons.org/croissant/",
        "data": {
            "@id": "cr:data",
            "@type": "@json"
        },
        "dataType": {
            "@id": "cr:dataType",
            "@type": "@vocab"
        },
        "dct": "http://purl.org/dc/terms/",
        "examples": {
            "@id": "cr:examples",
            "@type": "@json"
        },
        "excludes": "cr:excludes",
        "extract": "cr:extract",
        "field": "cr:field",
        "fileObject": "cr:fileObject",
        "fileProperty": "cr:fileProperty",
        "fileSet": "cr:fileSet",
        "format": "cr:format",
        "includes": "cr:includes",
        "isLiveDataset": "cr:isLiveDataset",
        "jsonPath": "cr:jsonPath",
        "key": "cr:key",
        "md5": "cr:md5",
        "parentField": "cr:parentField",
        "path": "cr:path",
        "rai": "http://mlcommons.org/croissant/RAI/",
        "recordSet": "cr:recordSet",
        "references": "cr:references",
        "regex": "cr:regex",
        "repeated": "cr:repeated",
        "replace": "cr:replace",
        "sc": "https://schema.org/",
        "separator": "cr:separator",
        "source": "cr:source",
        "subField": "cr:subField",
        "transform": "cr:transform"
    },

  "@type": "sc:Dataset",
  "name": "minimal_example",
  "description": "This is a minimal example."
}

mlcroissant validate --jsonld minimal.jsonld
W0924 14:42:44.972785 131393281629056 rdf.py:87] WARNING: The JSON-LD `@context` is not standard. Refer to the official @context (e.g., from the example datasets in https://github.com/mlcommons/croissant/tree/main/datasets/1.0). The different keys are: {'@language', 'samplingRate'}
Traceback (most recent call last):
  File "/home/adria/.pyenv/versions/ckan-dcat-310/bin/mlcroissant", line 7, in <module>
    sys.exit(main())
  File "/home/adria/.pyenv/versions/3.10.16/envs/ckan-dcat-310/lib/python3.10/site-packages/mlcroissant/scripts/cli.py", line 32, in main
    app.run(module.main)
  File "/home/adria/.pyenv/versions/3.10.16/envs/ckan-dcat-310/lib/python3.10/site-packages/absl/app.py", line 316, in run
    _run_main(main, args)
  File "/home/adria/.pyenv/versions/3.10.16/envs/ckan-dcat-310/lib/python3.10/site-packages/absl/app.py", line 261, in _run_main
    sys.exit(main(argv))
  File "/home/adria/.pyenv/versions/3.10.16/envs/ckan-dcat-310/lib/python3.10/site-packages/mlcroissant/scripts/validate.py", line 52, in main
    mlc.Dataset(jsonld, debug=debug)
  File "<string>", line 6, in __init__
  File "/home/adria/.pyenv/versions/3.10.16/envs/ckan-dcat-310/lib/python3.10/site-packages/mlcroissant/_src/datasets.py", line 89, in __post_init__
    self.metadata = Metadata.from_file(ctx=ctx, file=self.jsonld)
  File "/home/adria/.pyenv/versions/3.10.16/envs/ckan-dcat-310/lib/python3.10/site-packages/mlcroissant/_src/structure_graph/nodes/metadata.py", line 460, in from_file
    return cls.from_json(ctx=ctx, json_=json_)
  File "/home/adria/.pyenv/versions/3.10.16/envs/ckan-dcat-310/lib/python3.10/site-packages/mlcroissant/_src/structure_graph/nodes/metadata.py", line 470, in from_json
    jsonld = expand_jsonld(json_, ctx=ctx)
  File "/home/adria/.pyenv/versions/3.10.16/envs/ckan-dcat-310/lib/python3.10/site-packages/mlcroissant/_src/core/json_ld.py", line 258, in expand_jsonld
    recursively_populate_jsonld(entry_node, id_to_node, context)
  File "/home/adria/.pyenv/versions/3.10.16/envs/ckan-dcat-310/lib/python3.10/site-packages/mlcroissant/_src/core/json_ld.py", line 187, in recursively_populate_jsonld
    and value[0].get("@language", context["@language"])
KeyError: '@language'

One could argue it is a best practice defining a @language tag as fallback, but it is not mandatory as part of the JSON-LD or Croissant spec, so perhaps this particular check could be relaxed.