SIMBA and KNNFewShot optimizers

[tosinamuda]

User story
As a developer, I want SIMBA (and KNNFewShot) so I have the introspective/mini-batch optimizer surface DSPy offers beyond the flagship three.

Acceptance criteria

• SIMBA and KNNFewShot implemented.
• Their upstream teleprompt tests pass through the bridge.

Sub-tasks

• Port SIMBA's mini-batch introspection loop.
• KNNFewShot (needs the KNN retriever).
• Conformance.

[tosinamuda]

Deferred out of the 1.0 ceiling per the roadmap re-scope: KNNFewShot needs retrieval/embeddings and SIMBA is a heavy optimizer — both post-1.0. Tracked here, not killed.