[codex] Port tensor4all to tenferro main

[shinaoka]

Summary

• Update tensor4all-rs to build against the current tenferro-rs main API.
• Replace the old EagerContext/Engine flow with the new runtime, compiler, and executor APIs.
• Move einsum, QR, SVD, and solve call sites to the current tenferro-einsum/tenferro-linalg interfaces, while preserving tensor4all's column-major conventions.
• Update affected examples, benches, and dtype handling for the changed tenferro surface.

Refs #510.

Validation

• git fetch origin and verified branch base matches current origin/main (de480ba).
• cargo fmt --all
• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo nextest run --release --workspace (2348 passed, 14 skipped)
• cargo test --doc --release --workspace
• cargo doc --workspace --no-deps (completed; rustdoc emitted existing link warnings)
• ./scripts/test-mdbook.sh