Harden scientific envelope behavior for SciPy, Torch, and Sklearn

[bbopen]

Harden SciPy, Torch, and Sklearn envelope behavior so supported cases are explicit and unsupported cases fail clearly.

Acceptance Criteria

• supported envelopes and explicit failure behavior are documented and tested
• lossy or device-transfer behavior remains opt-in
• unsupported cases fail clearly instead of falling back silently