This commit fixes a bug where knowledge sources were being loaded eagerly
during agent/crew initialization, causing authentication errors (401) when
users didn't have proper credentials configured.
Changes:
- Modified Knowledge class to use lazy loading pattern
- Added _sources_loaded private attribute to track loading state
- Knowledge sources are now loaded only when first queried
- Removed eager add_sources() calls from agent.set_knowledge() and crew.create_crew_knowledge()
- Added comprehensive tests for lazy loading behavior
The fix ensures that:
1. Knowledge sources don't require authentication during initialization
2. Sources are loaded on-demand when actually needed (first query)
3. Subsequent queries don't reload sources
4. Explicit add_sources() calls still work as expected
Fixes#3764
Co-Authored-By: João <joao@crewai.com>
