Update aws-xray module to follow style guide

[Copilot]

This PR updates the AWS X-Ray module to align with the project's style guide requirements, focusing on minimal changes to improve code consistency and maintainability.

Changes Made

Test Class Visibility

• Changed ResourceHolderTest class and its testCustomized() method from public to package-protected, following the style guide recommendation that "Test classes and test methods should generally be package-protected (no explicit visibility modifier) rather than public"

Static Imports

Added static imports for commonly used constants as recommended by the style guide:

TimeUnit constants in main classes:

• AwsXrayRemoteSampler.java: Added static imports for SECONDS and NANOSECONDS
• AwsXrayRemoteSamplerBuilder.java: Added static imports for SECONDS and NANOSECONDS
• AwsXrayIdGenerator.java: Added static import for MILLISECONDS

Collections utilities in test classes:

• AlwaysRecordSamplerTest.java: Added static import for emptyList
• XrayRulesSamplerTest.java: Added static imports for emptyList, emptyMap, and singletonMap

Impact

• All existing functionality is preserved - no behavioral changes
• Code is more concise and readable with static imports
• Better adherence to project style conventions
• All tests continue to pass

The changes are surgical and minimal, touching only what's necessary to bring the module into compliance with the style guide.

Fixes #126.

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