Support CsvMerge to specify dtype parameter.(Fixes #647)

[skxeve]

Brief

Fixes #647

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• Any unexpected impact
• The overall quality is trending positively

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[x-chi]

[should]
You need to add an explanation of the new dtype parameter to the documentation, such as docs/modules/csv_merge.md.

[memo]
Invalid input to dtype: The Arguments class defines dtype: str | dict, but if a string or dictionary in an unacceptable format is passed to Pandas/Dask's read_csv, an exception will be raised at runtime.

[skxeve]

@x-chi
Thanks for the review!
I have updated docs/modules/csv_merge.md to include an explanation of the dtype parameter.

Regarding the exception when an invalid dtype is passed:
Since cliboa is an ETL framework, users typically identify such configuration errors during the initial testing phase of their scenarios. Therefore, I believe this behavior is acceptable.

Furthermore, strictly validating the dtype format to match the evolving specifications of Pandas or Dask would involve high maintenance costs. I think it is better to keep the constraints loose on the cliboa side and let the underlying libraries handle the specific validation.

Thank you for the feedback!

[x-chi]

Thank you for implementing it. I was also able to confirm the manual.