chore(ci): bump release workflow actions to Node 24 before 2026-09-16 deadline

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Context

GitHub is deprecating Node.js 20 on Actions runners per blog post:

• 2026-06-02 — Node 24 becomes default (actions with a Node 20 wrapper get forced to Node 24 unless opted out)
• 2026-09-16 — Node 20 removed from runners entirely (any unmigrated action hard-fails)

The v0.12.1 release run surfaced warnings for actions/checkout@v4 and actions/upload-artifact@v4 still bundling Node 20.

Scope

Update .github/workflows/release.yml and .github/workflows/ci.yml:

Current	Target	Notes
actions/checkout@v4	actions/checkout@v5	Node 24 bundle
actions/upload-artifact@v4	actions/upload-artifact@v5	Node 24 bundle, API-compatible
actions/download-artifact@v4	actions/download-artifact@v5	Node 24 bundle
actions/setup-node@v4	actions/setup-node@v5	Node 24 bundle
dtolnay/rust-toolchain@stable	verify upstream has Node 24 release	no explicit version tag
Swatinem/rust-cache@v2	verify upstream	cache format stable
softprops/action-gh-release@v2	verify upstream has Node 24 release

Acceptance

• Both workflow runs (release + CI) emit zero Node-20-deprecation warnings
• One dry-run release against a throwaway tag succeeds end-to-end (publish platform packages to npm + upload assets to GH release)
• No regression in cache hit rate (Swatinem/rust-cache)

Priority

Not urgent — 5 months of runway. Bundle into the next feature release that touches CI anyway.