Fixes#4525 - Telemetry was being sent even when tracing was disabled.
Changes:
- Check CREWAI_TRACING_ENABLED env var in _is_telemetry_disabled()
- Check has_user_declined_tracing() in _is_telemetry_disabled()
- Add regression tests for all disable mechanisms
- Fix env var leakage in existing telemetry test fixtures
Co-Authored-By: João <joao@crewai.com>