Update span-stacktrace module to follow style guide

[Copilot]

This PR updates the span-stacktrace module to align with the project's style guide requirements with minimal changes:

Changes Made

1. Added final keyword to public classes

• Made StackTraceSpanProcessor and StackTraceAutoConfig final per the style guide requirement that "Public non-internal classes should be declared final where possible"

2. Added static imports for logging levels

• Added static imports for Level.FINE and Level.SEVERE in StackTraceAutoConfig
• Updated usage from Level.FINE to FINE and Level.SEVERE to SEVERE following the style guide recommendation for commonly used constants

3. Made test class package-protected

• Removed public modifier from StackTraceAutoConfigTest to follow the guideline that "Test classes and test methods should generally be package-protected (no explicit visibility modifier) rather than public"

All changes maintain backward compatibility and the module continues to build successfully with all tests passing.

Fixes #284.

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:

• 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 -XX:MaxMetaspaceSize=512m -Dfile.encoding=UTF-8 -Duser.country -Duser.language=en -Duser.variant -cp /home/REDACTED/.gradle/wrapper/dists/gradle-9.0.0-bin/d6wjpkvcgsg3oed0qlfss3wgl/gradle-9.0.0/lib/gradle-daemon-main-9.0.0.jar -javaagent:/home/REDACTED/.gradle/wrapper/dists/gradle-9.0.0-bin/d6wjpkvcgsg3oed0qlfss3wgl/gradle-9.0.0/lib/agents/gradle-instrumentation-agent-9.0.0.jar org.gradle.launcher.daemon.bootstrap.GradleDaemon 9.0.0 (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)

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