fix(ci): require Rust 1.94.0 in Dockerfile via rustup

The rust:1.85-slim base image is too old for LazyLock and simd_caps.
Switch to debian:bookworm-slim + rustup install of 1.94.0 explicitly.

https://claude.ai/code/session_01CdqyUTUfjKZuk8YGJzv6LB

Author: claude

Dockerfile

@@ -1,18 +1,27 @@
 # ndarray — Railway compile-test image
 # Verifies the HPC module builds cleanly (default + jit-native features)
+# Requires Rust 1.94.0 (LazyLock, simd_caps, modern std APIs)
 #
 # Build: docker build -t ndarray-test .
 # Run:   docker run --rm ndarray-test
 
-FROM rust:1.85-slim AS builder
+FROM debian:bookworm-slim AS builder
 
-WORKDIR /app
-
-# System deps for Cranelift JIT
+# System deps
 RUN apt-get update && apt-get install -y --no-install-recommends \
-    pkg-config libssl-dev \
+    curl ca-certificates gcc libc6-dev pkg-config libssl-dev \
     && rm -rf /var/lib/apt/lists/*
 
+# Install Rust 1.94.0 via rustup
+ENV RUSTUP_HOME=/usr/local/rustup \
+    CARGO_HOME=/usr/local/cargo \
+    PATH=/usr/local/cargo/bin:$PATH
+RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | \
+    sh -s -- -y --default-toolchain 1.94.0 --profile minimal \
+    && rustc --version | grep -q "1.94.0"
+
+WORKDIR /app
+
 # Copy workspace files first for layer caching
 COPY Cargo.toml Cargo.lock ./
 COPY ndarray-rand/Cargo.toml ndarray-rand/Cargo.toml
@@ -34,4 +43,4 @@ RUN cargo test --release --lib -- hpc:: 2>&1 && echo "=== HPC TESTS OK ==="
 # Minimal runtime image — just proves it compiled
 FROM debian:bookworm-slim
 COPY --from=builder /app/target/release/libndarray.rlib /usr/local/lib/
-CMD ["echo", "ndarray build verified"]
+CMD ["echo", "ndarray build verified — Rust 1.94.0"]