feat: Add Rust/cargo build support

[Copilot]

Adds containerized Rust builds using cargo, following the established Go/Zig language build pattern.

Implementation

Core Package (pkg/rust/)

• Build orchestration with rust:1.83-alpine base image
• Build script generation for cargo commands with profile/target/features support
• Cache management via CARGO_HOME volume mounts
• Production image creation copying binaries from target/{profile}/

Pipeline Integration (cmd/engine.go)

• Registered rust.New() in Build category
• Registered rust.NewProd() in PostBuild category

Build Flow

Pull base images → Build Rust toolchain image → Execute cargo build + test → Commit with binary → Tag

Configuration

build := container.Build{
    BuildType: container.Rust,
    App:       "binary-name",
    Image:     "registry/image",
    ImageTag:  "v1.0",
}
build.Custom.Set("profile", "release")              // release|debug
build.Custom.Set("target", "x86_64-unknown-linux-musl")  // cross-compilation
build.Custom.Set("features", "tokio,serde")         // cargo features

Generated Build Script

#!/bin/sh
set -e
export CARGO_HOME=/root/.cargo
cargo build --color never --release --target x86_64-unknown-linux-musl
cargo test --color never --release --target x86_64-unknown-linux-musl

Files

• pkg/rust/rust.go - Container orchestration (304L)
• pkg/rust/buildscript.go - Script templating (130L)
• pkg/rust/buildscript_test.go - Unit tests (133L)
• pkg/rust/Dockerfile.rust - Base image definition
• Documentation in docs/RUST_*.md

Original prompt

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This section details on the original issue you should resolve

<issue_title>Support Rust build with cargo.</issue_title>
<issue_description>Check the golang and zig implementation how to implement a language build process with engine-ci.

For now also just focus on build on Linux with cargo.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Support Rust build with cargo. #380

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