Milestone 2: Add XML.toJSONObject(...) with replacement logic and test cases

[RJCheuk]

Summary

This pull request implements Milestone 2, Task 2 for SWE262P.

✅ Changes made:

• Added a new overloaded static method:
  XML.toJSONObject(Reader reader, JSONPointer path, JSONObject replacement)
• Implemented internal replacement logic in a new method:
  parseMilestone2(...)
• Modified XML parsing so that the replacement is done during parsing, without reading the entire XML content into memory first.
• Added a new test class:
  XMLPointerReplaceTest.java
  • Includes tests for:
    • successful replacement
    • invalid path
    • null reader

📌 Notes

• All existing test suites remain untouched and pass.
• The new test cases were added in src/test/java/org/json/junit/XMLPointerReplaceTest.java
• README-M2.md (not yet added) will explain the design and performance considerations in detail.

[sonarqubecloud]

Quality Gate failed

Failed conditions
32.6% Duplication on New Code (required ≤ 3%)
B Maintainability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

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[stleary]

Closed due to failing tests