Minimize faer features for strided einsum

[shinaoka]

Summary

• disable faer's broad default feature set at the strided-rs workspace boundary
• retain only the std and rayon features required by strided-einsum2
• add a dependency contract test preventing npy, sparse, and rand features from returning

This is the upstream dependency fix required by tensor4all/tenferro-rs#1397. strided-einsum2 remains the owner of strided dot-general execution; the change only narrows its provider dependency.

Verification

• cargo test --workspace
• cargo test -p strided-einsum2 --no-default-features --features faer,parallel --no-run
• cargo fmt --all --check
• cargo tree -p strided-einsum2 contains no npyz, py_literal, pest, sparse, or faer rand dependencies