Prevent overflow in sliding average updates

[krotname]

Motivation

• The rolling-window update used arr.get(i) - arr.get(i - windowSize) which performs 32-bit subtraction before adding to the long accumulator and can produce incorrect averages for edge-case int inputs.

Description

• Widen the incoming value before subtraction by changing the update to sum += (long) arr.get(i) - arr.get(i - windowSize); in SlidingAverage.movingAverage to ensure 64-bit arithmetic for the delta.
• Add a regression unit test extremeValuesDoNotOverflowTheRollingUpdate that verifies a transition from Integer.MIN_VALUE to Integer.MAX_VALUE with windowSize = 1 produces the correct values.
• Changes touch src/main/java/algorithms/sprint0/SlidingAverage.java and src/test/java/algorithms/sprint0/SlidingAverageTest.java and preserve existing behavior for non-extreme inputs.

Testing

• Ran the focused unit suite with mvn -B -Dtest=algorithms.sprint0.SlidingAverageTest test and the SlidingAverage test class passed (8 tests, 0 failures).
• Ran the full verification gate with mvn -B verify which completed successfully (all tests passed and build checks including coverage, Checkstyle, PMD, and SpotBugs showed no blocking issues).

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Codex Task

[krotname]

Superseded by the validated combined merge in #115: #115