Update safetensors-mojo to 0.7.0

[egor-fedorov]

Summary

Update safetensors-mojo from 0.5.0 to 0.7.0.

• Pin the recipe to the immutable commit behind the annotated v0.7.0 tag.
• Build and test on every native platform supported by Mojo 1.0.0: linux-64, linux-aarch64, and osx-arm64.
• Include local sharded Safetensors index support introduced in 0.6.0.
• Include the portable mapped I/O, atomic writing, and secure sharded path resolution work completed in 0.7.0.

Validation

• pixi run lint
• Direct recipe schema validation
• Render and solve for linux-64, linux-aarch64, and osx-arm64
• Native linux-64 package build and installed-package smoke test
• Source CI
• Release workflow

Checklist

• Recipe source is pinned to a full commit SHA.
• Build number remains 0 for the new upstream version.
• Package license metadata remains unchanged.
• MAX compatibility is not applicable; this is a standalone Mojo package.