added @SafeVarargs to ensure warnings error enabled on main

[ThyTran1402]

Description

Replace @SuppressWarnings("unchecked") with @SafeVarargs on all generic varargs methods across libs/core and libs/common.

Root cause: Methods with generic varargs parameters (e.g., Iterator<? extends T>..., E...) produce two distinct compiler warnings:
A declaration-site warning (-Xlint:varargs): "Possible heap pollution from parameterized vararg type"
A call-site warning (-Xlint:unchecked): "unchecked generic array creation for varargs parameter"

With -Werror enabled globally, any call site outside that scope remained exposed and could fail compilation on a cold build which is exactly what caused the Maven snapshot publication to break after #9120 was merged as mentioned in #9149.

Fix: Annotate each safe generic varargs method with @SafeVarargs at the declaration. This suppresses both warnings for all callers automatically and is semantically correct because none of these methods write typed elements back into their varargs arrays with no heap pollution.

Related Issues

Resolves #9150

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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PR Reviewer Guide 🔍

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🧪 No relevant tests

🔒 No security concerns identified

✅ No TODO sections

🔀 Multiple PR themes Sub-PR theme: Add @SafeVarargs to libs/common generic varargs methods Relevant files: libs/common/src/main/java/org/opensearch/common/collect/Iterators.java libs/common/src/test/java/org/opensearch/common/collect/IteratorsTests.java libs/common/src/main/java/org/opensearch/common/util/set/Sets.java Sub-PR theme: Add @SafeVarargs to libs/core generic varargs methods Relevant files: libs/core/src/main/java/org/opensearch/ExceptionsHelper.java libs/core/src/main/java/org/opensearch/core/common/util/CollectionUtils.java

⚡ Recommended focus areas for review SafeVarargs on Non-final @SafeVarargs on the package-private ConcatenatedIterator constructor is valid only if the constructor is not overridden. Since it is a constructor (not a method), this is fine. However, verify that ConcatenatedIterator is not subclassed anywhere, as @SafeVarargs on non-final, non-static, non-private methods would be a compile error in Java, but constructors are safe. Confirm no heap pollution risk exists in the constructor body. @SafeVarargs ConcatenatedIterator(Iterator<? extends T>... iterators) { SafeVarargs Correctness @SafeVarargs on unwrap is appropriate only if the clazzes varargs array is never written to or exposed in a heap-polluting way. The method iterates over clazzes using isInstance, which is safe. However, confirm that no subclass or override of this method writes to the varargs array, as @SafeVarargs does not propagate to overrides. @SafeVarargs public static Throwable unwrap(Throwable t, Class<?>... clazzes) {

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PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Impact
General	Retain suppressed unchecked warning on method The @SuppressWarnings("unchecked") annotation was removed from the convert method, but the method still uses an unchecked cast via Iterators.concat with a varargs call involving wildcard types. This may reintroduce an unchecked cast compiler warning that was previously suppressed. Verify that removing this annotation does not cause new compiler warnings or errors, and if so, retain the annotation. libs/core/src/main/java/org/opensearch/core/common/util/CollectionUtils.java [164-167] +@SuppressWarnings("unchecked") private static Iterable<?> convert(Object value) { return switch (value) { case Map<?, ?> map -> () -> Iterators.concat(map.keySet().iterator(), map.values().iterator()); case Iterable<?> iterable when value instanceof Path == false -> iterable; Suggestion importance[1-10]: 5 __ Why: The PR's intent is to replace @SuppressWarnings("unchecked") with @SafeVarargs where appropriate. The convert method itself doesn't use varargs, so @SafeVarargs doesn't apply here. However, since Iterators.concat now has @SafeVarargs, the unchecked warning at the call site may be suppressed by the callee's annotation, making the @SuppressWarnings on convert unnecessary. The suggestion to verify is valid but the concern may already be addressed by the @SafeVarargs on concat.	Low

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❌ Gradle check result for 98f884e: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?