TEMPORARY: only log cargo fingerprints on the build steps

The rust session parses `cargo test --no-run --message-format=json`
output, and the fingerprint log lines broke that. The recompiles this
is meant to catch happen in the maturin build, so log there only.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QZZQDQuPPD8T7jaAsCSHtM