ci: install taplo and cargo-machete from prebuilt binaries

[abnobdoss]

Which issue does this PR close?

• None. This is a CI maintenance change for the check job's tooling.

What changes are included in this PR?

The check job installs taplo and cargo-machete from source on every run: make check-toml runs cargo install --locked taplo-cli@0.9.3 and make cargo-machete runs cargo install cargo-machete@0.7.0. Compiling these tools from source costs roughly 2 minutes per run, on each OS in the check matrix.

This switches both to prebuilt binaries via taiki-e/install-action — the same mechanism the repo already uses for cargo-nextest (in the tests job) and cargo-public-api (in public-api.yml). The action downloads the published release binary instead of compiling it.

Concretely, in the check job this adds one install step and points the two checks at the installed binaries:

• taiki-e/install-action with tool: taplo@0.9.3,cargo-machete@0.7.0
• taplo fmt --check
• cargo machete

The pinned tool versions match what the Makefile installs today (taplo 0.9.3, cargo-machete 0.7.0), so the checks themselves are unchanged — only the install path differs. The Makefile targets are left as-is for local development.

Are these changes tested?

• Not run locally; this is a GitHub Actions workflow-only change.