Add CUDA resource ownership

[linear3735]

Purpose

Add Rust ownership of a CUDA device, stream and buffers. Check copy bounds and keep resources alive until pending work completes. CPU builds do not link CUDA.

Part of #14. This is the resource layer for Laya; model execution comes separately. Core and configuration changes: 271 lines.

Tests now live under the repository-root tests/ directory. Cargo target names and test coverage are unchanged.

Test Plan

cargo fmt --all --check
cargo clippy --workspace --locked --all-targets -- -D warnings
cargo test --workspace --locked
cargo build --workspace --release --locked

On H800, check allocation, a 4 KiB copy roundtrip and buffer lifetime after dropping the context handle.

System1-Omni Version / Commit: a20b2da91805d247141c50559021442a004a0e36.

Test Result

fmt, strict Clippy, release build passed locally; 25 CPU tests passed and 3 GPU tests were skipped. The existing H800 resource test passed against the same runtime source; this test-directory update does not change CUDA code.

Rust CI, Docs build and benchmark harness tests passed for this update.

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