GH-3587: Add DEBUG logging to BaseAdvisor implementations

[ranjitm2001]

Summary

This PR adds DEBUG level logging to the before() and after() methods of the following BaseAdvisor implementations:

• QuestionAnswerAdvisor
• VectorStoreChatMemoryAdvisor
• MessageChatMemoryAdvisor
• RetrievalAugmentationAdvisor

Changes

Each advisor now logs:

• In before(): The incoming query/request, number of documents retrieved, and any augmentation applied
• In after(): Processing of the response and any metadata added

Example Log Output

DEBUG [QuestionAnswerAdvisor] before: userQuery='What is Spring AI?'
DEBUG [QuestionAnswerAdvisor] before: retrieved 5 documents from vector store
DEBUG [QuestionAnswerAdvisor] before: augmented user message with 1234 characters of context
DEBUG [QuestionAnswerAdvisor] after: processing response
DEBUG [QuestionAnswerAdvisor] after: added retrieved documents metadata to response

Testing

• All existing tests pass
• Logging follows the same pattern as PromptChatMemoryAdvisor which already has logging

Closes gh-3587