Implement Java version of COBOL merge_sort_test.cbl

[devin-ai-integration]

PR Description

This pull request implements the Java version of the COBOL program merge_sort_test.cbl. The implementation includes the following classes:

• CustomerRecord: Represents the customer data structure with exact field sizes.
• FileReader and FileWriter: Handle fixed-width record I/O matching COBOL's behavior.
• MergeSortProcessor: Implements the merge and sort operations.

The program workflow includes:

• Generating test data into two input files (test-file-1.txt and test-file-2.txt).
• Merging files on ascending customerID into merge-output.txt.
• Sorting merged results on descending contractID into sorted-contract-id.txt.

Ticket ID: MBA-18

Link to Devin run: https://app.devin.ai/sessions/c7c6f573566a4418bc9b3ec459ee7d26

Requested by: Shawn Azman (shawn@cognition.ai)

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Devin Review found 1 potential issue.

View 3 additional findings in Devin Review.

[devin-ai-integration]

🔴 String.format does not enforce maximum field width, breaking round-trip with FileReader

In FileWriter.java:17, the format string "%-5s%-50s%-50s%-5s%-25s" uses minimum-width specifiers but does not enforce maximum widths. In Java, %-5s means "left-justify with minimum width 5" — if a string is longer than 5 characters, it will NOT be truncated. This means if any field value exceeds its designated column width (e.g., a customerID longer than 5 chars), the total line length will exceed 135 characters, and FileReader.java:20-24 will parse the fields at wrong positions, silently producing corrupt CustomerRecord objects. The fix is to use precision in the format specifiers: "%-5.5s%-50.50s%-50.50s%-5.5s%-25.25s".

Suggested change

	String line = String.format("%-5s%-50s%-50s%-5s%-25s",
	record.getCustomerID(),
	record.getLastName(),
	record.getFirstName(),
	record.getContractID(),
	record.getComment());
	String line = String.format("%-5.5s%-50.50s%-50.50s%-5.5s%-25.25s",
	record.getCustomerID(),
	record.getLastName(),
	record.getFirstName(),
	record.getContractID(),
	record.getComment());

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