ci: use setup-soldr to speed up fbuild workers

[zackees]

Goal

Use zackees/setup-soldr to speed up fbuild's GitHub Actions workers by replacing the repo's repeated manual soldr/rustup/cache setup with one action-managed setup step.

The action installs one released soldr binary, provisions the rust-toolchain.toml toolchain with rustup, and restores cacheable Soldr/Cargo/rustup state. It also has first-class caches for Soldr-owned zccache artifacts and Cargo target/ outputs.

Why this should help

Current fbuild workflows still pay repeated setup costs:

• check-ubuntu.yml, fmt.yml, docs.yml, msrv.yml, and template_build.yml install soldr manually with curl or pip.
• check-macos.yml, check-windows.yml, and template_native_build.yml checkout/build zackees/soldr from source before running fbuild checks/builds.
• template_build.yml manually wires actions/cache for package/build state.
• Native/build workers do not consistently get action-managed target/ and zccache artifact cache reuse.

setup-soldr can centralize this and remove duplicated bootstrapping logic while making worker cold/warm timings visible through cache outputs.

Proposed migration

Start with the Rust worker workflows, then fan out to board/native templates:

1. Replace manual soldr setup in these workflows with:

- uses: zackees/setup-soldr@v0
  with:
    cache: true
    build-cache: true
    target-cache: true
    toolchain-file: rust-toolchain.toml

2. Keep Rust commands as direct soldr commands, for example:

- run: soldr cargo check --workspace --all-targets
- run: soldr cargo clippy --workspace --all-targets -- -D warnings
- run: soldr cargo test --workspace

3. For native packaging workers, use explicit target-dir / lockfile inputs where needed so cross-target caches do not collide.

4. Remove duplicated manual install/build steps for soldr from:

   • .github/workflows/check-ubuntu.yml
   • .github/workflows/check-macos.yml
   • .github/workflows/check-windows.yml
   • .github/workflows/fmt.yml
   • .github/workflows/docs.yml
   • .github/workflows/msrv.yml
   • .github/workflows/template_build.yml
   • .github/workflows/template_native_build.yml

5. Add cache diagnostics to job summaries using action outputs where useful:

   • cache-hit
   • build-cache-hit
   • target-cache-hit
   • cache-restore-status
   • build-cache-restore-status
   • target-cache-restore-status

Acceptance criteria

• fbuild Rust check workers use zackees/setup-soldr@v0 instead of manual soldr install/build steps.
• fbuild board/native build templates use setup-soldr where compatible.
• target-cache and Soldr-owned zccache build-cache are enabled for workers where they reduce runtime without unsafe cross-target reuse.
• Existing soldr cargo ... commands continue to work unchanged after setup.
• Job logs or summaries expose setup/cache hit status so we can compare cold vs warm worker times.
• Remove old duplicated soldr bootstrap steps once each workflow is migrated.

Suggested validation

For each migrated worker type, compare before/after on one cold run and one warm rerun:

Workflow	Cold before	Cold after	Warm before	Warm after	Notes
check-ubuntu	TBD	TBD	TBD	TBD	Rust check/clippy/test
check-macos	TBD	TBD	TBD	TBD	currently builds soldr from source
check-windows	TBD	TBD	TBD	TBD	currently builds soldr from source
template_build board worker	TBD	TBD	TBD	TBD	package/build cache interaction
template_native_build	TBD	TBD	TBD	TBD	target-specific cache keys matter

Related

• Remove repo-local _* Rust tool wrappers and call soldr directly #181: make soldr the canonical Rust tool entry point and remove repo-local _cargo / _rustc / _rustfmt wrappers.
• [META] Fastest possible FastLED examples CI rebuild — profile + benchmark #112 / [META] fbuild build cache must survive CI tar-extract / cross-runner restore #147: broader cold/warm CI rebuild performance tracking.