[xgb] Fix xgb intern to close replaced array

[ewan0x79]

Description

close replaced array for xgb engine

[frankfliu]

This is not necessary, the instanceof will check null:

if (!(replaced instanceof XgbNDArray))

[frankfliu]

NDArray operation is not thread-safe. Adding synchronized here won't improve thread-safty

[frankfliu]

Not sure about this null check, if we want to prevent a closed NDArray, we should just do:

if (this.closed()

[frankfliu]

The memory leak issue may caused by alternativeArray leak, I think we should close current array's alternative array as will. The code can be re-implemented as the following:

        if (!(replaced instanceof XgbNDArray)) {
            throw new IllegalArgumentException(
                    "The replaced NDArray must be an instance of XgbNDArray.");
        }
        XgbNDArray array = (XgbNDArray) replaced;
        if (isReleased()) {
            throw new IllegalArgumentException("This array is already closed");
        }
        if (replaced.isReleased()) {
            throw new IllegalArgumentException("This target array is already closed");
        }

        long pointer = handle.getAndSet(0L);
        JniUtils.deleteDMatrix(pointer);
        if (alternativeArray != null) {
            alternativeArray.close();
        }

        data = array.data;
        handle = array.handle;
        format = array.format;
        alternativeArray = array.alternativeArray;
        array.handle = null;
        array.alternativeArray = null;
        array.close();

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 38.46154% with 8 lines in your changes missing coverage. Please review.

Project coverage is 72.40%. Comparing base (ca39062) to head (77fa14a).
Report is 14 commits behind head on master.

Files with missing lines	Patch %	Lines
...st/src/main/java/ai/djl/ml/xgboost/XgbNDArray.java	38.46%	4 Missing and 4 partials ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3558      +/-   ##
============================================
+ Coverage     72.36%   72.40%   +0.03%     
- Complexity     7410     7450      +40     
============================================
  Files           674      679       +5     
  Lines         33050    33290     +240     
  Branches       3521     3548      +27     
============================================
+ Hits          23918    24103     +185     
- Misses         7499     7540      +41     
- Partials       1633     1647      +14     

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