ci: automate releases with release-plz

Replace the 326-line semantic-release/npm workflow with release-plz, which
handles the whole chain the old one only half did:

- versioning and CHANGELOG from the conventional commits already in use
- a `chore: release vX.Y.Z` PR as the gate; merging it tags and releases
- publishes both crates to crates.io in dependency order, waiting for the
  index between them (RELEASE.md used to ask you to do this by hand)
- release-plz.toml keeps the two crates on one version, one tag, one changelog

Binaries now cover six targets instead of four. Linux switches from gnu to
musl so the downloads are statically linked and stop caring about the host's
glibc version; linux-aarch64 and windows-aarch64 are new. Archives carry
sha256 checksums plus README and LICENSE.

CI drops twelve hand-rolled actions/cache steps for Swatinem/rust-cache.

.github/workflows/ci.yml

@@ -22,23 +22,7 @@ jobs:
         with:
           components: clippy
 
-      - name: Cache cargo registry
-        uses: actions/cache@v4
-        with:
-          path: ~/.cargo/registry
-          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
-
-      - name: Cache cargo index
-        uses: actions/cache@v4
-        with:
-          path: ~/.cargo/git
-          key: ${{ runner.os }}-cargo-index-${{ hashFiles('**/Cargo.lock') }}
-
-      - name: Cache cargo build
-        uses: actions/cache@v4
-        with:
-          path: target
-          key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
+      - uses: Swatinem/rust-cache@v2
 
       - name: Run clippy
         run: cargo clippy --workspace --all-targets --all-features -- -D warnings
@@ -72,23 +56,7 @@ jobs:
         with:
           toolchain: ${{ matrix.rust }}
 
-      - name: Cache cargo registry
-        uses: actions/cache@v4
-        with:
-          path: ~/.cargo/registry
-          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
-
-      - name: Cache cargo index
-        uses: actions/cache@v4
-        with:
-          path: ~/.cargo/git
-          key: ${{ runner.os }}-cargo-index-${{ hashFiles('**/Cargo.lock') }}
-
-      - name: Cache cargo build
-        uses: actions/cache@v4
-        with:
-          path: target
-          key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
+      - uses: Swatinem/rust-cache@v2
 
       - name: Run tests
         run: cargo test --verbose
@@ -102,17 +70,7 @@ jobs:
       - name: Setup Rust
         uses: dtolnay/rust-toolchain@stable
 
-      - name: Cache cargo registry
-        uses: actions/cache@v4
-        with:
-          path: ~/.cargo/registry
-          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
-
-      - name: Cache cargo build
-        uses: actions/cache@v4
-        with:
-          path: target
-          key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
+      - uses: Swatinem/rust-cache@v2
 
       - name: Install SQLite runtime/dev libraries
         run: sudo apt-get update && sudo apt-get install -y libsqlite3-dev