Allow Setuptools detector to succeed with empty BOM when no dependencies found

[bd-spratikbharti]

Description

Summary

• Setuptools detector now succeeds with empty BOM when no dependencies are declared
• Aligns behavior with Maven, Gradle, NPM, and other detectors
• Fixes CI pipeline failures for Python projects without dependencies

Changes

• Added null check in SetupToolsTomlParser to handle missing [project].dependencies
• Modified resolveSetupToolsParser() to return default parser instead of null
• Removed SetupToolsNoDependenciesDetectableResult check from extractable()
• Added warning log when no dependencies are found