CI: use taiki-e/install-action for cargo tool installs

[avifenesh]

Audit Finding (DevOps, Medium)

Locations:

• .github/workflows/ci.yml:145 (iai-callgrind-runner)
• .github/workflows/security.yml:47 (cargo-audit)
• .github/workflows/fuzz.yml:47 (cargo-fuzz)
• .github/workflows/release.yml:48 (cross from git)

All four workflows install Rust tools via cargo install from source without caching. This wastes 2-10 minutes per run.

Fix: Use taiki-e/install-action which downloads prebuilt binaries with caching:

- uses: taiki-e/install-action@v2
  with:
    tool: cargo-audit@0.22.1

Found by /audit-project

[avifenesh]

Task completed successfully.

PR: #526
Status: Merged to main
Commit: fe8df5b

Summary

• Replaced all 4 remaining cargo install invocations in CI with taiki-e/install-action prebuilt binary steps
• All 11 tool installs now use the same SHA-pinned action
• Fixed step ordering in release.yml (cross install after rust-toolchain + rust-cache)
• Updated .github/workflows/README.md with correct SHA pin and fuzz.yml table entry

All CI checks passed. Merging completed.