build: add Checkstyle reporter for unused imports and trailing whitespace

[Kudwa-Abhishek]

Summary

• Added Checkstyle to the Maven build as a report-only validation step.

• Added checks for:

  • Unused imports
  • Trailing whitespace

• Enabled the checks for both main and test Java sources.

• Removed the unused imports identified by Checkstyle.

• Kept violations non-blocking so existing formatting issues do not introduce unrelated changes.

Testing

Ran:

mvn -B org.apache.maven.plugins:maven-checkstyle-plugin:3.5.0:check \
  -Dcheckstyle.config.location=src/checkstyle/checkstyle.xml \
  -Dcheckstyle.includeTestSourceDirectory=true \
  -Dcheckstyle.failOnViolation=false

Result:

BUILD SUCCESS

Also verified:

git diff --check

Result: no output / no whitespace errors introduced by this change.

Related issue: #139

[kabir]

Thank you @Kudwa-Abhishek !