Remove unused methods getFieldData() and getBigDecimal()

[yutaro-sakamoto]

This pull request makes minor code cleanups in the AbstractCobolField.java file by removing unused or placeholder methods. This PR will resolve #757

Most important changes:

Code cleanup:

• Removed the unused getFieldData() method, which contained placeholder logic for handling sign-separated and sign-leading attributes.
• Removed the unused getBigDecimal() method, which always returned BigDecimal.ZERO.

[Copilot]

Pull request overview

This PR performs code cleanup by removing two unused public methods from the AbstractCobolField class: getFieldData() and getBigDecimal(). Both methods were placeholders marked with TODO comments indicating they were "in preparation" (準備中), and searches confirm they are not referenced anywhere in the codebase, including subclasses and tests.

• Removed the getFieldData() method that returned CobolDataStorage with logic to handle sign-separated and sign-leading attributes
• Removed the getBigDecimal() method that always returned BigDecimal.ZERO

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[tsh-hashimoto]

Thank you.

getFieldData is certainly not referenced anywhere.

[ask]
getBigDecimal is also unused. However, java.sql.ResultSet does have a getBigDecimal method, and it is referenced in Select.scala in Open COBOL ESQL 4J.

https://github.com/opensourcecobol/Open-COBOL-ESQL-4j/blob/ff0bcf6bbbbcf88deaa3b69e1026aee25fb506ef/dblibj/src/main/scala/Select.scala#L222

Although they share the same name, I understand that they are unrelated (thus it can be deleted).
Please let me know if this assumption is correct.

[yutaro-sakamoto]

@tsh-hashimoto
getBigDecimal in java.sql.ResultSet and getBigDecimal in AbstractCobolField are unrelated