Fix #1001: Suppress spurious warning when including classpath config files without scan

[lukman48]

Summary

When a resource is included via <include resource="file.xml"/> without scan="true", logback would log an unnecessary INFO message about ConfigurationWatchList not being initialized. This produces spurious warnings in logs even though everything works correctly.

Root Cause

The addToWatchList() method was logging a message whenever ConfigurationWatchList was null, regardless of whether file monitoring was actually enabled.

Solution

Only log the message when createCWL=true (which indicates that an attempt was made to create a watch list). When createCWL=false (the default for <include> elements), silently return without logging, as file monitoring is not enabled and the classpath resource cannot be monitored anyway.

Changes

• Modified ConfigurationWatchListUtil.addToWatchList() to conditionally log based on createCWL parameter
• Added comprehensive test class ConfigurationWatchListUtilTest with 4 test cases covering:
  • No spurious messages when createCWL=false (Issue including file from classpath produces unavoidable warning? #1001)
  • Proper watch list creation when createCWL=true with watchable protocol
  • Existing watch list behavior remains unchanged
  • Default behavior validation

Benefits

✅ Cleaner logs: no spurious messages when scan="false" (the default)
✅ Expected behavior: resources from classpath without scan directive don't log warnings
✅ Maintains backward compatibility: existing watch list behavior unchanged
✅ All existing tests pass

Testing

• New test class: ConfigurationWatchListUtilTest.java (4 test cases)
• Existing test suite passes: IncludeModelHandlerTest validates includes work correctly
• Full logback-core test suite passes

Fixes #1001

[ceki]

@lukman48 IncludeModelHandler and ConfigurationWatchListUtil were reviewed and thoroughly modified in version 1.5.30. I think that this PE is no longer applicable.

Please close this PR if you concur.