Make dspy optional for EP

[dphuang2]

Note

Makes DSPy optional and avoids import-time failures when it's not installed.

• Removes dspy from core dependencies; adds [project.optional-dependencies].dspy extra and updates lockfile extras
• Updates eval_protocol/training/__init__.py to conditionally import DSPy modules, expose __all__, and raise a clear ImportError via __getattr__ when DSPy-dependent symbols are accessed without the extra

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