fix(ci): run cargo build/test inline instead of a missing action command

[jdfalk]

Summary

The Rust job in reusable-ci.yml invokes gha-ci-workflow-helpers with
command: rust-build and command: rust-test — but that action never
implemented either command. Only rust-format and rust-clippy exist, in
every release through v1.1.7. So every repository whose Rust CI actually runs
dies at the build step:

##[error]Unknown command: rust-build

reusable-ci.yml was migrated to call action commands that were never added to
the action. This is fleet-wide — any repo with active Rust CI hits it.

Change

Build Rust project and Test Rust project now run cargo build --release /
cargo test --release inline. Format and Lint keep using the action, which
does support rust-format / rust-clippy.

Kept minimal deliberately — no --locked (would fail any repo with a drifted
lock) and no --all-targets (would force-build benches that some repos gate on
nightly).

Context

Surfaced by falkcorp/cockroach-rollout-agent, whose Rust CI activated for the
first time during the TODO fan-out (its Cargo.lock changed, and Rust CI was
skipped on its main before). Verified the crate itself is clean:
cargo clippy --all-targets -- -D warnings, cargo build --release, and
cargo test all pass locally — the failure was purely this missing-command bug.

Note this is distinct from #333 (the stale ghcommon-script pin): these Rust
commands run through the external action, not the checked-out scripts, so the
pin refresh didn't touch them.

actionlint clean.

🤖 Generated with Claude Code

https://claude.ai/code/session_013vU67T2LJDCbYTBs9ZFAf2