Fix JSON writes to fsspec targets

[fallintoplace]

Summary

• pass the opened fsspec file object to the cuDF JSON writer
• add a memory:// regression test

This follows the existing CSV and ORC fsspec writer handling.

Testing

• pre-commit run ruff --files python/cudf/cudf/io/json.py python/cudf/cudf/tests/input_output/test_json.py
• pre-commit run ruff-format --files python/cudf/cudf/io/json.py python/cudf/cudf/tests/input_output/test_json.py
• python3 -m py_compile python/cudf/cudf/io/json.py python/cudf/cudf/tests/input_output/test_json.py

[copy-pr-bot]

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[mroeschke]

/ok to test aebf9ac