Stub out sim-rs/net-rs/shared-rs after move to leios-tools
These three Rust workspaces now live in their own repository, cardano-scaling/leios-tools, extracted with full git history. Replace each directory's contents with a short README pointing at the new home, and remove the now-orphaned build/CI that referenced the deleted source: - .github/workflows/sim-rs.yaml — built sim-rs (moved). - .github/workflows/conformance-linear.yaml — built sim-rs and ran the linear conformance check against sim-rs/parameters (moved). - .github/workflows/net-node-docker.yaml — built the net-node docker image from net-rs/ + shared-rs/ (moved; docker CI lives in leios-tools). - Dockerfile — drop the Rust build stage (rs-builder) and the `rs` target image that compiled sim-cli from sim-rs/. The Haskell `hs` image is unchanged. Stale prose/comment references remain in .dockerignore, topology-viewer/scripts/build-viewer-data.py, and a couple of config comments; left untouched here as they don't break the build. Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>