Make enabled fields volatile in SdkTracer, SdkMeter, and MetricStorage implementations

[Copilot]

Following the pattern established in open-telemetry#7706 for SdkLogger, this PR makes the enabled fields volatile in SdkTracer, SdkMeter, and MetricStorage implementations to ensure that configuration changes to disabled/enabled state are eventually visible across threads, as required by the OpenTelemetry specification update.

Changes Made

• SdkTracer.java: Changed tracerEnabled from protected boolean to protected volatile boolean and removed the outdated performance comment
• SdkMeter.java: Changed meterEnabled from private boolean to private volatile boolean
• DefaultSynchronousMetricStorage.java: Changed enabled field from private boolean to private volatile boolean
• AsynchronousMetricStorage.java: Changed enabled field from private boolean to private volatile boolean

Background

The OpenTelemetry specification requires that changes to disabled configuration must be eventually visible. Previously, these fields were deliberately non-volatile for performance reasons, which meant configuration updates might not be visible across threads in a timely manner. The decision was made to prioritize correctness over the marginal performance benefit.

This change ensures consistency across all SDK components (logs, traces, and metrics) and enables proper dynamic configuration updates at runtime.

Testing

All existing tests continue to pass, confirming that the behavioral changes maintain backward compatibility while providing the required eventual visibility guarantees.

Relates to open-telemetry#7706

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• dl.google.com
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.lang.invoke=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-opens=java.base/java.nio.charset=ALL-UNNAMED --add-opens=java.base/java.net=ALL-UNNAMED --add-opens=java.base/java.util.concurrent=ALL-UNNAMED --add-opens=java.base/java.util.concurrent.atomic=ALL-UNNAMED --add-opens=java.xml/javax.xml.namespace=ALL-UNNAMED --add-opens=java.base/java.time=ALL-UNNAMED -XX:MaxMetaspaceSize=512m -Dfile.encoding=UTF-8 -Duser.country -Duser.language=en -Duser.variant -cp /home/REDACTED/.gradle/wrapper/dists/gradle-9.1.0-bin/9agqghryom9wkf8r80qlhnts3/gradle-9.1.0/lib/gradle-daemon-main-9.1.0.jar -javaagent:/home/REDACTED/.gradle/wrapper/dists/gradle-9.1.0-bin/9agqghryom9wkf8r80qlhnts3/gradle-9.1.0/lib/agents/gradle-instrumentation-agent-9.1.0.jar org.gradle.launcher.daemon.bootstrap.GradleDaemon 9.1.0 (dns block)
• scans-in.gradle.com
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.lang.invoke=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-opens=java.base/java.nio.charset=ALL-UNNAMED --add-opens=java.base/java.net=ALL-UNNAMED --add-opens=java.base/java.util.concurrent=ALL-UNNAMED --add-opens=java.base/java.util.concurrent.atomic=ALL-UNNAMED --add-opens=java.xml/javax.xml.namespace=ALL-UNNAMED --add-opens=java.base/java.time=ALL-UNNAMED -XX:MaxMetaspaceSize=512m -Dfile.encoding=UTF-8 -Duser.country -Duser.language=en -Duser.variant -cp /home/REDACTED/.gradle/wrapper/dists/gradle-9.1.0-bin/9agqghryom9wkf8r80qlhnts3/gradle-9.1.0/lib/gradle-daemon-main-9.1.0.jar -javaagent:/home/REDACTED/.gradle/wrapper/dists/gradle-9.1.0-bin/9agqghryom9wkf8r80qlhnts3/gradle-9.1.0/lib/agents/gradle-instrumentation-agent-9.1.0.jar org.gradle.launcher.daemon.bootstrap.GradleDaemon 9.1.0 (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

@open-telemetry/opentelemetry-javaopen-telemetry/pull/7706

Should make this to relevant places for SdkTracer, SdkMeter (and MetricStorage impls)

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