chore: pin mlx-swift-lm 3.31.8
Bumps the exact mlx-swift-lm pin from 3.31.5 to 3.31.8.
3.31.8 (cut from runanywhere-3.31.5-maple) adds decision-checkpoint support: joint schema head, canonical prompt/span encoding, and ClefDecisionModel. The SDK's top-level pin moves to 3.31.8 in the same change, so this exact-version dependency must move in lockstep or SPM resolution fails (exact 3.31.5 vs exact 3.31.8).
Needs a follow-up release tag (0.1.6) once merged — please tag when you merge; I do not have push access to this repo.
Summary by cubic
Updates the pinned mlx-swift-lm dependency from 3.31.5 to 3.31.8 in Package.swift, which adds decision-checkpoint support. The SDK's top-level pin moves in the same change, so the exact-version dependency must move in lockstep or SPM resolution fails. Requires a follow-up 0.1.6 release tag after merge.