Rewrite in Rust (#3)

Just what the world needs, another silly Rust re-write! But it was a good exercise in learning.

There's a lot of messy things, which is why this is 0.2.0-pre.1. Going to make some cleaning passes after landing this.

.github/workflows/rust.yml

@@ -0,0 +1,37 @@
+name: Rust
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Cache
+      uses: actions/cache@v4
+      with:
+        path: |
+          ~/.cargo/registry
+          ~/.cargo/git
+          target
+        key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+
+    - name: Rust version
+      run: rustup --version
+    - name: Check
+      run: cargo check
+    - name: Clippy
+      run: cargo clippy
+    - name: Build
+      run: cargo build
+    - name: Run tests
+      run: cargo test