Jsonpolars

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**Minor Improvements**

- Add the missing jskit module. This module provides a lot of syntax sugar.

**Bugfixes**

**Miscellaneous**

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**Features and Improvements**

- Allow to use the polars liked chain syntax to create the expression.

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**Bugfixes**

- Fix a bug in ``StructField`` that when ``name`` is a single string, it should be interpreted as a single field, not a list of field.

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**Features and Improvements**

- Now all ``BaseDfop`` and ``BaseExpr`` has a stable ``to_dict()`` and ``from_dict()`` method.
- Now all ``BaseDfop`` and ``BaseExpr`` constructor will automatically use the polars default value if the user does not pass the value.

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**Minor Improvements**

- Add ``PolarsTypeNameEnum`` to public API, so user don't need to type the polars type string manually.

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**Features and Improvements**

- From dict now no need to pass value for those fields with default value
- Cast dtype should be str, not polars DataType