Stop the Linux CI job running out of disk, and cut its runtime

The ubuntu-latest job has been failing since at least 1 Aug, on unrelated
dependabot PRs as well. The annotation is

    Unhandled exception. System.IO.IOException: No space left on device :
    '.../actions-runner/extracted/_diag/Worker_....log'

The runner died writing its own diagnostic log, which is why the step logs
are absent and the job's steps are still reported as in_progress.

Three profiles of the same rattler-scale tree accumulate in rust/target
before the existing `rm -rf rust/target` mitigation runs: debug from the
editable install, instrumented from coverage, and release from `make build`.
Locally that directory reaches 7.0G without a coverage run.

- Free disk space: drops the unused Android/dotnet/GHC/Swift toolchains.
  Taken verbatim from the upstream template, which added it in b93abda after
  hitting the identical failure on another project; it reported free space
  going from 7G to 30G. nepenthe is 68 commits behind the template and its
  scheduled copier update has been failing, so it never received this.

- Build: skipped on Linux. `make dist-rs` runs the same `cargo build
  --release`, and cibuildwheel then rebuilds from scratch in the manylinux
  container, so this was a third compile of the same tree and a third copy of
  it on disk. Still runs on macOS and Windows, where nothing else covers it.

- cargo-nextest / cargo-llvm-cov: installed as prebuilt binaries rather than
  compiled from source on every run. `cargo install --force` rebuilt them
  unconditionally; nextest alone took 9m35s of the 24m dependency step. The
  make target now skips them when they are already on PATH, so it no longer
  undoes the prebuilt install, and repeat local runs get the same saving.

Author: timkpaine

.github/workflows/build.yaml

@@ -45,6 +45,14 @@ jobs:
 
     - uses: actions-ext/rust/setup@main
 
+    # `make develop` compiles these from source otherwise, ~10 minutes a run.
+    # These are the prebuilt binaries; the Makefile skips its own install when
+    # they are already on PATH.
+    - name: Install cargo tools
+      uses: taiki-e/install-action@cb33e69fad06166ca28a42b2575e4dadabf62ee8 # v2.85.8
+      with:
+        tool: cargo-nextest,cargo-llvm-cov
+
     - name: Install dependencies
       run: make develop
 
@@ -55,8 +63,12 @@ jobs:
       run: make checks
       if: matrix.os == 'ubuntu-latest'
 
+    # On Linux `make dist-rs` rebuilds this same release profile, and
+    # cibuildwheel then rebuilds the tree again from scratch in the manylinux
+    # container, so building here is a third compile and a third copy on disk.
     - name: Build
       run: make build
+      if: matrix.os != 'ubuntu-latest'
 
     - name: Test
       run: make coverage
@@ -85,6 +97,13 @@ jobs:
         platforms: all
       if: runner.os == 'Linux' && runner.arch == 'X64'
 
+    - name: Free disk space
+      run: |
+        sudo rm -rf /usr/local/lib/android /usr/share/dotnet /opt/ghc /usr/local/.ghcup /usr/share/swift
+        df -h /
+      shell: bash
+      if: matrix.os == 'ubuntu-latest'
+
     - name: Make dist (Linux)
       run: |
         rm -rf dist

rust/Makefile

@@ -3,8 +3,8 @@
 requirements:  ## install required dev dependencies
 	rustup component add rustfmt
 	rustup component add clippy
-	cargo install --locked --force cargo-nextest
-	cargo install --force cargo-llvm-cov
+	command -v cargo-nextest >/dev/null || cargo install --locked cargo-nextest
+	command -v cargo-llvm-cov >/dev/null || cargo install cargo-llvm-cov
 
 develop: requirements  ## install required dev dependencies