fix: report outdated resource deletion failures

[efegokdemir]

Fixes #517

Summary

EarMojo now reports a warning when an outdated work-directory resource cannot be deleted, instead of silently continuing with stale output.

Changes

• Check the return value of File.delete() in deleteOutdatedResources.
• Log the affected resource when deletion fails.

Testing

• JAVA_HOME=/opt/homebrew/Cellar/openjdk/27/libexec/openjdk.jdk/Contents/Home mvn -DskipITs -Dspotless.check.skip=true -Dspotless.apply.skip=true verify — passed; 48 tests passed.
• git diff --check — passed.
• Checkstyle and RAT passed; four existing Checkstyle findings were ignored by the repository configuration.
• Integration tests were not run because -DskipITs was used for the focused local validation.

Notes

The change is intentionally limited to observability of deletion failures; it does not change the cleanup policy or mask the failure. AI assistance was used in preparing this change; I reviewed the modified code and test results.

• I hereby declare this contribution to be licensed under the Apache License Version 2.0, January 2004.