Ryo Kitagawa

Hi @goccy! Thank you for the great library! I'd like to propose support for a new built-in ZetaSQL function like the one referenced here: https://github.com/google/zetasql/blob/a516c6b26d183efc4f56293256bba92e243b7a61/zetasql/public/builtin_function.proto#L1349 It seems the current go-zetasql...

fix: convert to datetime64[us] when TIMESTAMP or DATETIME is empty

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Fixes #852 In the document, pandas-gbq returns `datetime64[ns]` or `object`, but in pandas2, it returns `datetime64[us]`. https://googleapis.dev/python/pandas-gbq/latest/reading.html#inferring-the-dataframe-s-dtypes 

Timestamp returns a different type depending on whether the data is empty or not.

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#### Environment details - OS type and version: macOS sonoma 14.6 - Python version: 3.11.9 - pip version: I use rye instead of pip. and rye version is 0.35 -...

add lines parameter to JsonFileProcessor

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I think auto enabled lines is a bit confusing. So, I think it is preferable to specify `lines=True` explicitly.

Check default value type of Parameter

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Check default value of parameter. ```python import luigi import gokart class MyTask(gokart.TaskOnKart): foo = luigi.IntParameter(default='s') # Incompatible default for argument "foo" (default has type "str", argument has type "int") ```

Timestamp returns a different type depending on whether the data is empty or not.

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#### Environment details - OS type and version: macOS sonoma 14.6 - Python version: 3.11.9 - pip version: I use rye instead of pip. and rye version is 0.35 -...

## Summary This PR adds support for polars DataFrames alongside pandas DataFrames in gokart's file processors. Ta sks can now specify their DataFrame type via the `TaskOnKart[T]` type parameter, and...