feat: add CusumDetector, cumulative sum change detection for streams

[alxkm]

CUSUM change detection

Adds CUSUM (cumulative sum) change detection. The repository has no change or
drift detection yet.

A threshold on raw samples only catches changes that are large compared with the
noise. CUSUM accumulates evidence instead: each sample is normalised to
z = (x - target) / sigma and pushed into two one-sided sums.

upper <- max(0, upper + z - k)
lower <- max(0, lower - z - k)

The allowance k is a toll paid on every step. On target, the toll exceeds the
average evidence, so both sums stay pinned at zero and the detector stays quiet
however long it runs. Once the mean shifts by more than k standard deviations,
the matching sum drifts up until it crosses the threshold h. A half-sigma
shift is invisible in a single sample but clear after twenty. O(1) time and
state per sample.

ShiftSignal is included because accept and scan return it.

CusumDetectorTest covers 16 cases. The two that matter most: a stream on
target raises no alarm over 100,000 samples, and in-control Gaussian noise gives
at most 2 false alarms in 2,000 samples — while a half-sigma drift is still
caught within 60 samples.

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new algorithms include a corresponding test class that validates their functionality.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.30508% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.84%. Comparing base (ad10eda) to head (4bf82be).

Files with missing lines	Patch %	Lines
...ava/com/thealgorithms/streaming/CusumDetector.java	98.30%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7593      +/-   ##
============================================
+ Coverage     80.78%   80.84%   +0.05%     
- Complexity     7597     7625      +28     
============================================
  Files           819      820       +1     
  Lines         24320    24379      +59     
  Branches       4775     4783       +8     
============================================
+ Hits          19648    19710      +62     
+ Misses         3907     3906       -1     
+ Partials        765      763       -2     

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